[rbd246]

Hello all, Im new to these forums and just registered.
I plan to be an active participant on here and reciprocate the generosity I've observed in other threads.

Im looking for a certain "material" that can satisfy this list of criteria that I've put together.
I'm pretty sure that Im looking for a polymer but perhaps someone else has some other suggestions (all of which are most welcome).
So here are the criteria:
-i would like to be able to embed or "en-vein" in this material a few heating coils/wires
-can absorb heat but not melt while doing so. these coils/wires would be heated and expected to heat this material in which they're
embedded. (not talking about too high a temperature here, I'd only like it to stay around 80-85 degrees farenheit) the heat would be
expected to spread from the coil/wire to and through it's surrounding material.
-can be able to retain some of that heat and not easily lose it to the air around it.
-If slightly stretched/stressed/pressed, in any way, it wouldn't easily crack/break/tear or rip.
-If feet were to be set ontop of this "mat of material" it would feel comfortable and soft (not a pudding soft, but a firm soft...
if that makes sense, haha).
-hydrophobic - if a cup of water were to be spilled near this "mat of material" it wouldn't seep through this material and damage or
disrupt the inner coils/wires.
-while being warm and soft, it shouldn't feel dry to one's feet but rather smooth.
-if this material were lying around and a man/woman were to be breathing in the air, this material wouldn't somehow be "toxic"
or hazardous to one's health via something airborne relating to the nature of this material. also it shouldn't produce some bad rash
or other reactive response from a person's touch/feet.

Ideally someone could name what it is I'm looking for and suggest me a way to acquire it.
Just as good would be any suggestions, advice, or input that would help me get a little closer to that ideal.

Thanks all and looking to be an active CF member!

[Enthalpy]

Welcome, rbd246!

All polymers have roughly the same heat capacity and conductivity. Heat transfer to the air is limited by the air, not the plastic. So these criteria leave all polymers nearly equal.

Embedding the resistors should be done with great care. Especially, long thin wire would look very bad to my intuition, because heat would have little area to escape the wires, creating hot spots near the wires. You must also consider the possibility of bubbles or voids at the interface, which shouldn't burn then. I'd strongly prefer resistors with a big surface, for instance printed under the polymer, or a thin metal evaporated onto rods which are embedded in the polymer.

In any case, I'm quite wary about heating a plastic, and much worse near people - see the number of deaths by heating blankets. Some plastics don't burn in air (Underwriter Laboratories have an index for this behaviour), but nearly all emit toxic fumes when hot or burnt by nearby materials.

I also dislike putting electricity under people's feet. Safety standards allow in under easy conditions, but consider children may cut your soil with a knife for instance... Could you at least embed a layer of Nomex or some Aramide above the resistors? You may have seen some at yellow fabric gloves used at home ovens.

For both reasons, I'd strongly prefer to heat separately an insulating fluid which then circulates in tubes embedded in your soil. An independent sensor can check the fluid's temperature just at the heater's exit to shut off power under abnormal conditions, and electricity stays away from people.

Most plastics feel comfortable to the feet. Elastomers are softer - available in any hardness you want, often expressed as Shore, where Shore C, Shore A, Shore 00... are different scales. But flammability, toxicity when lukewarm, toxicity when burning will limit the choice to nearly nothing - especially if price is a limit. May children play for hours sitting on your soil?

Simplifying a little bit, all plain plastics and elastomers are hermetic, as opposed to foams or fabrics. Until they're scratched, you can wash them with litres of water without shorting embedded conductors. But once cut, you've lost - one more reason to embed a very strong fabric like aramide above the conductors.

[rbd246]

Welcome, rbd246!

All polymers have roughly the same heat capacity and conductivity. Heat transfer to the air is limited by the air, not the plastic. So these criteria leave all polymers nearly equal.

Embedding the resistors should be done with great care. Especially, long thin wire would look very bad to my intuition, because heat would have little area to escape the wires, creating hot spots near the wires. You must also consider the possibility of bubbles or voids at the interface, which shouldn't burn then. I'd strongly prefer resistors with a big surface, for instance printed under the polymer, or a thin metal evaporated onto rods which are embedded in the polymer.

In any case, I'm quite wary about heating a plastic, and much worse near people - see the number of deaths by heating blankets. Some plastics don't burn in air (Underwriter Laboratories have an index for this behaviour), but nearly all emit toxic fumes when hot or burnt by nearby materials.

I also dislike putting electricity under people's feet. Safety standards allow in under easy conditions, but consider children may cut your soil with a knife for instance... Could you at least embed a layer of Nomex or some Aramide above the resistors? You may have seen some at yellow fabric gloves used at home ovens.

For both reasons, I'd strongly prefer to heat separately an insulating fluid which then circulates in tubes embedded in your soil. An independent sensor can check the fluid's temperature just at the heater's exit to shut off power under abnormal conditions, and electricity stays away from people.

Most plastics feel comfortable to the feet. Elastomers are softer - available in any hardness you want, often expressed as Shore, where Shore C, Shore A, Shore 00... are different scales. But flammability, toxicity when lukewarm, toxicity when burning will limit the choice to nearly nothing - especially if price is a limit. May children play for hours sitting on your soil?

Simplifying a little bit, all plain plastics and elastomers are hermetic, as opposed to foams or fabrics. Until they're scratched, you can wash them with litres of water without shorting embedded conductors. But once cut, you've lost - one more reason to embed a very strong fabric like aramide above the conductors.

WOW...My chemistry professor just told me "go look at polymers" and sent me on my way.
But you Enthalpy have proven beyond generous! Thank you SO much! I am simply amazed at how in-depth and comprehensive a response you've provided me It will take me some time to dissect this response for all it has to offer but once again I would like to give you my utmost gratitude and although I don't know too much about chemistry I will try in some ways to help out and contribute on here.
Thanks Enthalpy!!

[typhoon2028]

Embedding heating coils in a material is fairly commonly.  Heated floors is an example.

Urethane would probably work.  You could use a foamed plastic.  Higher density would be best.

Your heating coils could be sandwiched in between two layers of foam.  Polyolefin type foam can be easily heat bonded.