After doing many builds/saves in TPT that simulate the construction of real-world devices and machines that of course are entirely destroyable (therefore they must be destroyable in TPT as well), I have found that the game is lacking a material which can simulate the construction of a solid coating or wrap that can help maintain the rigidity and structure of certain materials. We have the Shield element which acts as a coating, however this isn't always "realistic" in the sense that it conducts electricity to repair itself and impervious to all forms of damage, short of high pressure.
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There are many metals I use in builds to make my breakable machines a little more resistant to common pressure damage and heat, however these are conductive and can cause issues in a save that uses a lot of electrical systems. (Sparks jump from one wiring set to a metal casing, etc). Quartz works good, that is, until it is kept at a low temperature in which it falls apart. Also, it tends to grow when touching water, so it's not optimal for containing liquids. Brick and Goo work, but their weakness is pressure. There are other examples I can throw out there, but these are the most common materials that lack the characteristics of what Carbon Fiber (reinforced polymer) could do for TPT.
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Carbon Fiber would act as such:
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-Have a high heat tolerance
-Impervious to moderate pressures
-Non-conductive (see insulation element)
-Slightly absorbs pressure (similar to Titanium)
-Neutral to most other elements (Ie., acid doesn't corrode it easily)
-forms hairline fractures when heated to extreme temps and exposed to high pressure
-unique appearance, easily distinguishable as carbon fiber
-(new) hairline fractures break down into coal or broken glass?
-acts similarly to a non-flammable insulation element
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This post is obviously up for discussion, but I feel as though it would be perfect for filling the gap between heat/pressure tolerance and rigidity and maintaining it's role as a breakable material that replaces conductive metals, as some saves require a material that is resistant to heat/pressure and is also non-conductive. I will edit the post once more ideas come to mind or are presented by other users.

I'm not certain as to what material it should break down into, perhaps broken glass? I think that would be the best choice in materials. And as for it being a more durable insulator, that's a great idea. It would fill the divide quite well. And thank you NUCLEAR_FOX.

And I'm just R3APER. I don't use any alts by that name.

The only issue is coal is flammable, unlike carbon which is largely inert and does not react to any other materials. IRL, coal would be fairly relatable to my understanding, however TPT doesn't follow the similarities quite as well. A sub-material could be created to replicate the broken carbon fiber, so maybe a 2 for 1 element addition to the game. Who knows. I just hope this catches traction with the mods. The last element I pushed for being created was Gel and that made it in, so we will wait and see. I'm not sure this will get enough attention or users backing the idea as not many people see my reasoning for adding it.