# insulated shipping boxes



## gary1218 (Dec 31, 2005)

It seems to me that everybody that uses an insulated shipping box uses foam insulation as the insulator. Anybody use anything else that provides better insulation?

I've seen some foam insulation products that are wrapped in an aluminum foil. Anybody ever doing any testing on those?

Are there things out there but they're not used because of the cost?


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## NathanB (Jan 21, 2008)

I've gotten plants before that had both a foam and the foil. Even though it was cold they came in fine.


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## Eric Walker (Aug 22, 2009)

I only use the molded foam boxes. I wouldn't do any peiceing of foam sheeting to insulate boxes because of the seams.

I go to my local hospital every so often to check and see what they have.
they get all sorts of sizes and thickness. they just pile them up in a closet untill they can find a way to get rid of them. most dont have a box on the outside. this can be a problem depending on how you ship, but its not to hard to find a box thats close in size. most of the boxes are a bit bigger which equates to a higher shipping cost as well. 

the boxes are free, so thats awsome. And what better than a medical quality shipping box.


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## Dancing frogs (Feb 20, 2004)

I've tested some vacum insulated boxes, with favorable results...more expensive, (around $45 each) but much more effective. Haven't had a chance to do a whole lot with it yet though...been busy with other things. More later...


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## james67 (Jun 28, 2008)

this is about the standard from my experience. reasonably priced IMO(and they sell excelsior by the bail too)

Insulated Shipping Kits

james


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## frogmanroth (May 23, 2006)

Someone sent me frogs with fiberglass housing insulation. I guessed it worked fine frogs were alive. And it was fairly cold out.


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## Brotherly Monkey (Jul 20, 2010)

james67 said:


> and they sell excelsior by the bail too


what's it listed under?


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## MichelleSG (May 1, 2010)

Brotherly Monkey said:


> what's it listed under?


Excelsior, put it in the search box


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## Brotherly Monkey (Jul 20, 2010)

MichelleSG said:


> Excelsior, put it in the search box


I already did that (did it again upon your recommendation)and it didn't return any results. i also checked under "paper products" and "cushioning, peanuts and foam"


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## MichelleSG (May 1, 2010)

Try Aspen, that got me excelsior


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## Brotherly Monkey (Jul 20, 2010)

MichelleSG said:


> Try Aspen, that got me excelsior


Never mind, my script blocker was on. But the help is still appreciated


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## gary1218 (Dec 31, 2005)

If you guys want to talk about excelsior could you do it in another post. Thanks.


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## pl259 (Feb 27, 2006)

VIPs and aerogels are the Cadillacs of the insulation world these days.


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## sports_doc (Nov 15, 2004)

No testing Gary but....

The foil wrap is to 'reflect' heat back. So have to have a heat source on the inside.

IMO in winter a nice combo would be an inner box with gel/ PCM and the frogs.

Then a larger outer box with foil wrapped insulation panels [get from HD and cut yourself] with the heat packs sandwiched b/t the two box layers.

An alternative is a solid styro box, wrap the frogs in gel and PCM. line the inside with foil and tape the heat packs to the lid or sides. Cross your fingers and ship..

S


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## Roadrunner (Mar 6, 2004)

or to reflect cold out w/ the foil facing out and a gel pack inside to release at a slower rate.
Heat kills and sterilizes and the window is small for what heat they'll tolerate. I have had frozen frogs arrive and thaw and be fine, I have also had frogs cook because the heat pack was too much. Too cold is better than too hot w/ 12 hours in transit.


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## sports_doc (Nov 15, 2004)

More info here

Frequently Asked Questions about Radiant Barrier Foil Insulation

Midwest energy savers - Foil insulation - Radiant Barriers - Cedar Rapids, IA

Radiant barrier insulation: questions and answers

Advantages of Reflective Foil Insulation over Bulk Insulation


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## sports_doc (Nov 15, 2004)

I dont disagree Aaron, it may be a ver delicate balance to achieve.

I've had now on 3 occasions had someone send me 'frozen' frogs, that did NOT thaw. 

Maybe the best option is some garage testing again Gary ? 

Traditionally the 40 hour heat packs are said to raise the ambient temp of an insulated box by 10-15F over an outside temp of 30F. So, 2 heat packs needed for a 20F box to get to a safe temp of 45-50F, yes?

The trick is to keep the temp long enough to last the trip

, not to cook the frogs if they are inside at 70F for a while in transit,

, and to protect them from direct heat exposure [by wrapping them in gel packs and PCM

thoughts?


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## Roadrunner (Mar 6, 2004)

I guess I'd face it in w/ a gelpack and out w/ a heat pack as it seems it can get too hot if it's all reflecting in w/ a heatpack.

I guess I'd have to see the boxes, have to know the temps they shipped them in and your temps when they arrived, who they shipped thru, etc.etc.etc.

I drop my frogs off at the airport around 10pm and they arrive by 10am. I have shipped in teens weather and haven't had problems w/ styro coolers of about 1 1/2 inches w/ heat pack inside but never used reflective insulation. I think the biggest part is completely sealing the insulation w/ tape or something so that pressure changes will not make for ANY air exchange as this will make any insulation somewhat useless. Also the use of many gelpacks is important to hold the temperature as the mass is much larger to make the amount of energy needed to change he temperature as great as possible. I don't think that any packages get exposed to outside temps for their whole trip if any depending on time on the tarmac. I think the instances of frozen frogs are from misplacement in a non pressurized chamber and not as much from regular conditions. Just my thoughts from a very few shipping problems over the years(most of which when I tried to save money using usps as I don't think I've had one problem since ups). I do always look for a shipping window as to not use heat packs though. Temps don't matter here as they are on a plane and out within an hour after dropping them off. They are usually 2 hours out in the elements when tehy go on the truck and if they don't experience cold till then they have a lot of time to overheat and the packs are usually at their lowest when they are exposed to the cold for the longest time.


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## Roadrunner (Mar 6, 2004)

I think this is true if the box starts at 20f and is exposed to 30f the whole way but does not take into account mass and airspace and insulation or reflective material. 

I personally think if they were packed in 70f temps and had reflective insulation and didn't hit 30f the whole way they would cook.

I would also put the heat pack on top of a gel pack which is on top of the frogs as this will distribute the heat thru the gelpack and not have the hot surface able to touch the frogs as they can reach 120f and this is how my frogs got cooked and the smell was terrible when I opened the box.


sports_doc said:


> Traditionally the 40 hour heat packs are said to raise the ambient temp of an insulated box by 10-15F over an outside temp of 30F. So, 2 heat packs needed for a 20F box to get to a safe temp of 45-50F, yes?


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## gary1218 (Dec 31, 2005)

pl259 said:


> VIPs and aerogels are the Cadillacs of the insulation world these days.


Eric,

How about a little more info on these.


I've definitely gone away from the heat packs. I'm a big believer in the 1lb PCM gel packs I get from 
Saf-T-Pak - 2 per box in a double insulated box works most often for me.

Shawn - I have been doing a lot of "garage testing" lately. For that reason it's looking more & more to me that the insulation isn't really the key. It's looking more & more to me that it's the PCM gel packs.

I'm hoping to get some more info from Brian on the vacuum insulated boxes he mentioned in his post.


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## Dancing frogs (Feb 20, 2004)

frogfarm said:


> or to reflect cold out w/ the foil facing out


If I'm not mistaken, that is backwards. I don't think cold can be "reflected".
An HVAC/refrigeration person will tell you "there is no such thing as cold, only an absence of heat".


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## Dancing frogs (Feb 20, 2004)

I've been making my own boxes (gluing them together) out of the foil faced polycyanurate (or whatever it is) for a while now, foil faced on both sides. 1.5" of it is upposed to have the same R rating as 2" of Polystyrene.

One thing to remember about working with the foil...aluminum is one of the best conductors of heat out there...if you intend on incorporating it with your packing scheme, avoid having any strips of foil that lead from the inside to the outside of the box...doing so provides a good pathway for your heat to escape/or get in, as the case may be.

On the vacum packaging...
A test in the freezer (9F) with 6 panels of phase 22 held above 60F for 27 hours.
The sample I received for testing is very roomy inside, but the outside of the box is smaller than the average frog shipper, as the insulation is only a half inch thick.
They offer a smaller box, but it is much smaller, and would be more expensive to purchase the minimum case size.

I had thought about arranging a group buy...they are in the neighborhood of $45 each.


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## gary1218 (Dec 31, 2005)

Dancing frogs said:


> A test in the freezer (9F) with 6 panels of phase 22 held above 60F for 27 hours.


This is what makes me think the key is the phase 22/PCM gel packs. I can get those types of results using the usual foam insulation with 2 of the 1lb soft gel PCM gel packs I get.

But if I switch out the PCM gel packs for 2 regular gel packs of the same size the frogs would be DOA.


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## Dancing frogs (Feb 20, 2004)

Yeah, the phase change material is key.

I ditched heat packs shortly after my first tests of the phase 22.

As mentioned earlier, the packages in shipment do not see outdoor temps for very long at all...this was confirmed on some tests we did shipping a temp logger in an uninsulated box.
Therefore, many people may be convinced their packing method works well, when in actuality, it is just the overnight service keeping their cargo alive.

When I first started shipping, I used a heat pack inside a molded styro box, taped shut...had good results (results being the frogs arriving alive). When I actually took the time to test the packaging (how it performs at temperatures) I was very surprised to find my packaging wasn't very effective at all.

I did a simulation once, with a heat pack (well started, and producing heat) put it in a sealed container (equal or greater than typical free air in a frog box)...at room temperature, the heat pack ceased to produce any heat at all in under an hour.
Long story short, the heat packs need air to work, it is a delicate balance to provide that air, and still provide a well insulated box, it can be done, but at the end of the day, phase change materials are much easier, work way better, and are worth every penny in my honest opinion.


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## Dancing frogs (Feb 20, 2004)

Wish I had closed on my new house last week...could have done a back yard test at -23F
Just for kicks...


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## pl259 (Feb 27, 2006)

frogfarm said:


> ...or to reflect cold out w/ the foil facing out





Dancing frogs said:


> If I'm not mistaken, that is backwards. I don't think cold can be "reflected".
> An HVAC/refrigeration person will tell you "there is no such thing as cold, only an absence of heat".


I got a chuckle out of that one too!


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## sports_doc (Nov 15, 2004)

I'm of the opinion that the heat packs added to the box, will help 'support' the PCM by providing at least some added energy to the system.

The PCM does not have a limitless ability to absorb or give off energy. Eventually it does indeed change phase.

Neither works perfect alone IMO, unless you are willing to pack a lot of PCM [cost and shipping wt prohibitive]

So, I use both.

Prove me wrong....


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## gary1218 (Dec 31, 2005)

sports_doc said:


> The PCM does not have a limitless ability to absorb or give off energy. Eventually it does indeed change phase.


That is definitely true. But, in my testing, it doesn't occur over the time that normal overnight shipping takes. Haven't really tested to see how long it would really take to hit that phase change.

Now, if the packages gets lost in overnight shipping I guess that's a different story. But even if that case I would give my shipping box a very good chance of still keeping the frogs warm. In my testing I'm sure for the most part I'm exposing my box to more cold than it would see during normal shipping.



sports_doc said:


> Neither works perfect alone IMO, unless you are willing to pack a lot of PCM [cost and shipping wt prohibitive]


You don't need a lot of PCM to be effective. But even just the 2 I use cost me $25. So, it really isn't practical to use them unless the buyer is willing to return them to you. I haven't had any issues with people doing this. They all realize it's for the safety of the frogs and are fine with it.


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## Roadrunner (Mar 6, 2004)

The whole idea was to NOT reflect the heat back in. Hope no frogs got hurt while you were chuckling and missing the point.



pl259 said:


> I got a chuckle out of that one too!


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## Roadrunner (Mar 6, 2004)

I think Eric missed your question Gary.


gary1218 said:


> Eric,
> 
> How about a little more info on these.
> 
> ...


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## Roadrunner (Mar 6, 2004)

Since Eric would rather chuckle than help you out, this is what I've found Gary.
The second one is in Macedon, NY.

BARRIER Ultra-R Aerogel Vacuum Insulation Panels (VIPs)- Thermal Insulation.

Therm-Max™ - Contact Us


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## pl259 (Feb 27, 2006)

gary1218 said:


> Eric,
> How about a little more info on these.
> ...
> 
> I'm hoping to get some more info from Brian on the vacuum insulated boxes he mentioned in his post.


I looked at VIPs(vacuum insulated panels) a couple years ago, but the cost was prohibitive. Bascially the same idea as the "vacuum insulated boxes", that a vacuum will not conduct or convect heat energy. Reflective surfaces are added to block radiant energy, in both directions. VIPs had the greatest R factors at the time. Something like 5 or 6 times the basic rigid foam panels.

Aerogels are starting to come out more now, but they too are expensive. Something like $10-$15 per square foot. Their R factor is about twice that of current rigid foam. Last I saw, they came in semi-rigid sheets. 

I expect that aerogels will start making their way into construction more and more. Their cost should drop. VIPs tend to be rigid and fixed in size, therefore more of a specialty product. For me it's been mostly a wait and see.


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## pl259 (Feb 27, 2006)

Hey Aaron, try googling "heat transfer" too. You might learn something. 
And while you're at it, learn to laugh at yourself a little more.


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## Roadrunner (Mar 6, 2004)

Already did as you didn't read my follow up post. I said I would face it in w/ a gelpack instead of a heatpack. Read quite extensively on a couple different websites about it.

I have no problem laughing at myself. If a friend said that to me I would've.



pl259 said:


> Hey Aaron, try googling "heat transfer" too. You might learn something.
> And while you're at it, learn to laugh at yourself a little more.


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## gary1218 (Dec 31, 2005)

I'd love to get my hands on some of those VIP panels to do some "garage testing"


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## pl259 (Feb 27, 2006)

Another point about VIPs is that they have a definate usable life span. Last I remember, the life was a couple/three years or so. Maybe they're better now. They basically leak tiny amounts over time which lowers their R values. 

One thing you mentioned Gary, was that you didn't think that insulation was a key factor here. That really goes against the physics as I understand it. What test(s) did you run to think that was the case?

Regarding foil, way back when, I did a couple simulations with a program called TAS. The amount of radiant heat loss was low, something like 5%. Foil might buy back some performance, but not much. Where the foil is placed makes a different too. For heat loss problems, which is what cold shipping is about, foil placed on the inside of the insulation should give better results then if placed outside the insulation. Foil tests would be interesting experiments to run.


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## gary1218 (Dec 31, 2005)

pl259 said:


> One thing you mentioned Gary, was that you didn't think that insulation was a key factor here. That really goes against the physics as I understand it. What test(s) did you run to think that was the case?


THANKS for all the info Eric.

I probably didn't state correctly what I meant about the insulation. Certainly the insulation is important but it didn't appear to be the determining factor in getting the frogs to their overnight destination all warm and cozy on a cold winters night.

I've been doing some "garage testing" in weather where the temps are somewhat cold, maybe 20's to 30's. So, cold but not extreme. I've been testing small to medium sized single and double insulted boxes, 1 1/2" to 2 1/2" thickness of insulation, with regular gel packs and the PCM gel packs. Even double insulated boxes with 2 large regular gel packs pre-heated to 78-80F wouldn't have kept the frogs from freezing to death. I'm sure the more insulation the longer they would have lasted. But I think it would have had to be a very thick layer of insulation to keep them alive for the whole overnight trip.

On the other hand, even the single insulated boxes with 1 large PCM gel pack would have kept the frogs warm enough to survive the overnight trip.

So for the way most of us ship our frogs it seems to me that the PCM gel packs are the key.

Now, before somebody starts jumping all over me about these not being "highly controlled scientific tests", let me just say you are 100% correct. These are just the casual observations of an interested hobbyist that wants to ship his frogs the best and most reasonable way possible


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## Dancing frogs (Feb 20, 2004)

I think I know what Gary was getting at with the insulation.

Tested in a controlled environment (my freezer), boxes of similar internal volume, with varying degrees (thickness) of insulation, with no buffer (heat storage), they all (I tested 2",1.5", and 1" inch) reached ambient temperature very quickly (can't remember exactly, but it was well under an hour, I wanna say more like half an hour), the difference in how quickly they reached ambient temp was very minute, we are talking minutes.

Not to say it is not important, just pointing that out.

I should be a poster model for backing up data...I'm on my 4th pc since I did a lot of these tests...lots of good, highly informative, controlled test logs are long gone.


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## Dancing frogs (Feb 20, 2004)

And from that info, it should be noted that insulation alone doesn't provide much protection, except from rapid temp change. Over an hour of exposure at a dangerous temp using nothing but average insulation, with no buffer, you are treading thin ice.


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## pl259 (Feb 27, 2006)

So the basic factors involved here are:

mass
specific heat of the mass
area of the outside of the box
R factor of the insulation

...and of course temperature difference between inside vs. outside the box

Throw them into a form of Newton's Law of Cooling, and you can solve for the temperature at some point after you start the experiment. It's an exponential decay as the temp inside drops and finally equals the outside temp. 

Those basic factors, mass, specific heat, area, and R factor, are all equally weighted. For example, doubling the mass will have the same effect as doubling the R factor. If we conduct an experiment to compare the effects of R factor alone(insulation), we have to hold all other factors the same, including outside area.

In our case, all shippers charge more for more mass. FedEx and UPS do the dimensional weight thing so bigger boxes, with their bigger areas, cost more. USPS has an advantage here. That's why I see insulation as the next, very important thing to watch for our needs. PCMs are great too, but they're effectiveness is about at their peak, IMO. Insulation is that factor that we can still go after to net some significant improvements. 

Ultimately, all of these factors buy us more time. Shipping time. More shipping time equals less shipping cost. There are many "Cold Chain" suppliers that already know these things. They're driving this bus and we should be able to go along for the ride and benefit from it too.

Sorry for the long post BTW...

Another thing we haven't talked about is active temperature control. Passive insulated masses are one thing. But throw in a heat pack or some batteries and electronics, and we have a whole other thing. Very easy to do. My only concern here is the flags it might raise when packages go through xray and thermal scans. But that's another thread I think.


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## gary1218 (Dec 31, 2005)

Dancing frogs said:


> I think I know what Gary was getting at with the insulation.
> 
> Tested in a controlled environment (my freezer), boxes of similar internal volume, with varying degrees (thickness) of insulation, with no buffer (heat storage), they all (I tested 2",1.5", and 1" inch) reached ambient temperature very quickly (can't remember exactly, but it was well under an hour, I wanna say more like half an hour), the difference in how quickly they reached ambient temp was very minute, we are talking minutes.


Yea..........what he said  Thanks Brian.

Eric, I need to come hang out with you for a day


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## Roadrunner (Mar 6, 2004)

What would be more useful than any of this is the actual temps the frogs are exposed to in transit. They may be able to make it to a pickup station and be fine w/ very little insulation if they are less than 15 minutes on tarmacs of 40f or higher. Of course more insulation will always lessen temperature swings but if you don't know the conditions they are going thru you can't accurately judge what's needed. Usually the trip to the house is the one that kills(or being put in an unpressurized cabin at -50f). The last 2-3 hours in a truck in 20f weather makes all the difference in the world. I have had frogs survive 8 days in ground transport. If boxes are stacked and the frogs are on the inside of a bunch of other boxes then they are much more insulated against the cold.
Below is the single most important variable.



pl259 said:


> So the basic factors involved here are
> 
> ...and of course temperature difference between inside vs. outside the box


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## gary1218 (Dec 31, 2005)

frogfarm said:


> but if you don't know the conditions they are going thru you can't accurately judge what's needed.


For me that's why I feel the PCM gel packs I use are so invaluable. No matter what the shipping box is experiencing on the outside the PCM gel packs are constantly working to keep the space where the frogs are at a constant temp in the mid 70's.


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## Dancing frogs (Feb 20, 2004)

gary1218 said:


> For me that's why I feel the PCM gel packs I use are so invaluable. No matter what the shipping box is experiencing on the outside the PCM gel packs are constantly working to keep the space where the frogs are at a constant temp in the mid 70's.


Exactly, and they don't produce heat, the way traditional heat packs do (or are intended to).
That way, if the box sits in a heated area longer than expected, no worries (about the package getting overheated) whatsoever...it just lengthens the protection time.

As per Eric's comment about box surface area, I take that into account as well when I make my custom boxes, and always choose a cube shape when possible (least surface area per volume).

I've been pondering battery powered, thermostatic heat for a long time. I know there are sweaters, mittens and socks that have heat with thermostats in them that have a selection that would be nearly appropriate for our needs (lowest setting is still a touch too warm) but the finished product is quite expensive, around $90 when I was looking a year or two ago.

Another thing, that no one really talks about, that would require inhumane tests to determine:
What temperature threshold is absolutely required to be maintained for x amount of time to keep the frogs alive and healthy?

If you could perhaps get away with 50F as a low threshold, vs 72F (just for example), and had phase change material appropriate for that range, in theory, the same mass would be able to hold above 50 for much longer than a similar mass above 72F.

You might read that and say, well duh, but the point is that the greater extreme of difference between inside and outside, the greater the rate of change.

To put it more simply, an equal mass of phase change material that changes phase at 50 would maintain above 50 for much longer than the same mass of phase change material that changes phase at 72.

That being said, I'm perfectly happy with phase 22 for winter shipments, but have pondering using something with a slightly higher melt for summer.

Some more ideas...


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## pl259 (Feb 27, 2006)

I agree with all of these comments. The coolest thing about PCMs is that they have a period of time where they "regulate" temps. It doesn't matter what the outside temps are, up to a point. 

Constructing a thermostatically controlled heater is easy. It should be able to be done for way less than $90. If there's interest in it I can start working on it. Energizer AA lithiums have 4W-Hr of capacity. A four cell pack, 16 W-Hr. That would provide a lot of reserve heat in an insulated box.


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## Dancing frogs (Feb 20, 2004)

pl259 said:


> I agree with all of these comments. The coolest thing about PCMs is that they have a period of time where they "regulate" temps. It doesn't matter what the outside temps are, up to a point.
> 
> Constructing a thermostatically controlled heater is easy. It should be able to be done for way less than $90. If there's interest in it I can start working on it. Energizer AA lithiums have 4W-Hr of capacity. A four cell pack, 16 W-Hr. That would provide a lot of reserve heat in an insulated box.


I may be interested, can you estimate a ballpark figure of cost and how effective it would be at reasonable temps, plus a weight, size estimate.
I usually draw the line at 20F for a low shipping with pcm. I think coupling the battery heat with pcm would offer the best degree of safety.
I probably wouldn't be interested in purchasing right away though...lots on my plate with a pending move.


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## Allyn Loring (Sep 30, 2008)

Ahhhhhhh fellows thought this was an "insulated boxes" thread lol


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## Ed (Sep 19, 2004)

Dancing frogs said:


> I've been pondering battery powered, thermostatic heat for a long time. I know there are sweaters, mittens and socks that have heat with thermostats in them that have a selection that would be nearly appropriate for our needs (lowest setting is still a touch too warm) but the finished product is quite expensive, around $90 when I was looking a year or two ago.


I just had a amusing thought of the news media release about the first package that was x-rayed before being allowed onto a plane and then detonated due to the belief the wiring, batteries etc looked too much like a bomb... 



Dancing frogs said:


> Another thing, that no one really talks about, that would require inhumane tests to determine:
> What temperature threshold is absolutely required to be maintained for x amount of time to keep the frogs alive and healthy?
> 
> If you could perhaps get away with 50F as a low threshold, vs 72F (just for example), and had phase change material appropriate for that range, in theory, the same mass would be able to hold above 50 for much longer than a similar mass above 72F.


We actually don't have to do inhumane testing on the frogs.. there is a body of literature already out there where tests have been done for critical thermal minima and maxima. I haven't looked yet, but even if there haven't been any studies on dendrobatids, you should be able to locate other anuran species from the same region to get an approximation. 

For example the critical Tmin for marine toads is around 43 F (which is too low).... if we also add in anecdotal examples as a source we should be get a good ball park.. for example I've had D. tinctorius easily survive 50 F and I think Lars reported that his auratus tolerated cooler temperatures. One of the things to keep in mind is that in other amphibians, the temperature at which they were housed for the last several weeks can change the Tmin and the rate of change of the temperature can be more of an issue than the absolute lowest temperature. 

Sorry for the ramble but a lot of thoughts running into one another... 

Ed


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## Dancing frogs (Feb 20, 2004)

Ed said:


> I just had a amusing thought of the news media release about the first package that was x-rayed before being allowed onto a plane and then detonated due to the belief the wiring, batteries etc looked too much like a bomb...
> 
> 
> 
> ...


Haha...it would look just like one too. Good point!


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## pl259 (Feb 27, 2006)

I have a $25 COTS solution in mind and should have some ready for testing in a couple weeks. These aren't a finished product, just a cobbled together tech demo that we can use to test the concept.


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## pl259 (Feb 27, 2006)

Dancing frogs said:


> I may be interested, can you estimate a ballpark figure of cost and how effective it would be at reasonable temps, plus a weight, size estimate.
> I usually draw the line at 20F for a low shipping with pcm. I think coupling the battery heat with pcm would offer the best degree of safety.
> I probably wouldn't be interested in purchasing right away though...lots on my plate with a pending move.


I've got a working test unit ready if you want to try out it's effect. It weights about 9oz, is digitally controlled, puts out about 2W for 4hrs continuous and cost about $25. I slapped it together for a test, but would need some final tweaking. All from off the shelf stuff. 

The idea would be to attach the heating element to a PCM and set the temp for, say 65F. When the temp inside the box drops below that, it'll come on and heat the PCM. The PCM and thermostat will prevent it from over heating the box, but it should extend the usable shipping times of a well insulated box. Testing will tell us how much. All it would take is more batteries to make it longer.

PM me if you want me to ship it out to you. You'll laugh at how simple it is. I'm not interested in selling them, but we can post a DIY if it works out.


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