Best insulation for a food carrier

[Chef Gilbert]

I would appreciate any advice on finding the best insulation material for my food carrier. 
I have been testing an insulated reusable/returnable one hand-held carrier design to hold freshly prepared food hot as to be delivered. It works, but the heat retention is insufficient. The temperature is good for 45 minutes. It is made of blow molded polyurethane. I want to improve the heat retention to as long as possible, two hours! I have tested ways to maintain the food for a fresh appearance. 
Numerous material were tested, money was spent and lessons were learned. High-density Styrofoam, low cost, in different applications had good insulation quality but required too many layers of protection inside the chamber and out as well. The inside layer was warping.

My question: Is polyurethane the only insulation material to be blow molded and self-skinning? 
Here are the basic requirements:
Material must sustain high heat on contact
Material cannot warp 
The material must be the best insulation ( two hours!)
The method/material must be self-skinning (blow molding ?)
Lightweight as to be carried with one hand
Cost-effective reusable/returnable
Must sustain heavy commercial traffic
Must be NSF approved.
I am open to any suggestion and will answer any question.  
Thanks

Chef Gilbert

[Phi for All]

Is there a way to place a thin sheet of reflective foil material so the vacuum mold presses it to the inside of the carrier? This would provide a radiant barrier so heat stays trapped inside, and the food should stay hotter longer. Then your current insulating material can be used. This might not solve your warping problem, since food touching the foil will still conduct heat.

Also, is there any way to place the handles on the bottom half instead of the lid half? I picture people picking this up and having dinner drop to the ground.

[Frank]

One thought is it could use a radiation heat loss layer on the inside surface - like an aluminium layer or MLI - https://en.wikipedia.org/wiki/Multi-layer_insulation

Not sure what the best way to accomplish this is - inner container or maybe painted on.

The other thought is to use an insulated bag around multiple units.  The bag would have the required insulation thickness and would be used during transport.

The last thought is to actively add heat via a battery, like a hunting jacket/socks.

One more is to use a material that can retain heat and heat that before putting in the food.  Or a phase change material that can be activated closer to readiness time.

 

[StringJunky]

The interior would be better white or mirror-like metal because it's more reflective whereas black is more absorptive. If it's a single-layer container then two or three layers with air gaps in between would be better. The containers want to be pre-warmed prior to putting the food in so that the heat within the food is not used to warm it up initially; that's like pouring hot water into a cold cup.

[koti]

 

51 minutes ago, Chef Gilbert said:

I would appreciate any advice on finding the best insulation material for my food carrier. 
I have been testing an insulated reusable/returnable one hand-held carrier design to hold freshly prepared food hot as to be delivered. It works, but the heat retention is insufficient. The temperature is good for 45 minutes. It is made of blow molded polyurethane. I want to improve the heat retention to as long as possible, two hours! I have tested ways to maintain the food for a fresh appearance. 
Numerous material were tested, money was spent and lessons were learned. High-density Styrofoam, low cost, in different applications had good insulation quality but required too many layers of protection inside the chamber and out as well. The inside layer was warping.

My question: Is polyurethane the only insulation material to be blow molded and self-skinning? 
Here are the basic requirements:
Material must sustain high heat on contact
Material cannot warp 
The material must be the best insulation ( two hours!)
The method/material must be self-skinning (blow molding ?)
Lightweight as to be carried with one hand
Cost-effective reusable/returnable
Must sustain heavy commercial traffic
Must be NSF approved.
I am open to any suggestion and will answer any question.  
Thanks

Chef Gilbert

All I can think of is some form of an active system...like a small portable source of heat that would keep the food warm. 2 hours seem to be far too long to keep the food warm just with passive methods especially in cold weather conditions. From the top of my head, what I'd do is use one of those standard food carriers which pizza delivery uses and stick a heat source inside - 6 good quality 18650 LiOn rechargeable batteries (the ones used in your laptop) could easily provide a heat source capable of sustaining proper food temperature for hours. Just hook up the batteries to a bunch of thin copper wires put a control chip with a thermostat to control the temperature according to conditiins. The delivery guy could hook up the carrier to recharge after he’s done with the delivery. This kind of setup could serve you a couple of years without the need to replace the cells. 18650’s have at least 500 discharge cycles on them before they need replacement. You coukd custom build this or Im sure somebody manufactures a simillar product.

Edited December 30, 2017 by koti

[Chef Gilbert]

Phi, Very good observation regarding the handles. The food is placed in a casserole dish which stays in when placed on the dining table. Designed to keep food hot while eating. If handles are on the bottom it would not be a good appearance, but, yes we had only a couple of accident until we did a demonstration on how to handle it. Then, no more problem.
In a previous design, the reflective material was used and was effective. Thanks for the advice.

 Frank, I have done some testing with pre-heating the top cover part, yes, it was effective and solved the condensation problem.
Thanks

StringJunky, Yes, agree. See above with reflective material top and bottom.
Thanks

koti, Good thinking, but I need to keep things simple first that's why I am looking for a better insulation and avoid some serious cost. 
Thanks to all.

Chef Gilbert

 

 

[StringJunky]

What about this professional insulated pizza delivery bag to put the containers in.

https://thermalbags.com

[Frank]

 

 

9 hours ago, Chef Gilbert said:

Phi, Very good observation regarding the handles. The food is placed in a casserole dish which stays in when placed on the dining table. Designed to keep food hot while eating. If handles are on the bottom it would not be a good appearance, but, yes we had only a couple of accident until we did a demonstration on how to handle it. Then, no more problem.
In a previous design, the reflective material was used and was effective. Thanks for the advice.

 Frank, I have done some testing with pre-heating the top cover part, yes, it was effective and solved the condensation problem.
Thanks

StringJunky, Yes, agree. See above with reflective material top and bottom.
Thanks

koti, Good thinking, but I need to keep things simple first that's why I am looking for a better insulation and avoid some serious cost. 
Thanks to all.

Chef Gilbert

 

 

Since the top is being heated, the bottom could house a phase change material like a sodium acetate heating pad which would hold more heat and could also be activated on demand:

https://en.wikipedia.org/wiki/Sodium_acetate#Heating_pad