Insulation Gaskets Material??

What 3M material are these made from? I want to buy some to want to make my own non-conductive washers out of this material.

Not 100%, but my guess is “polyethylene terephthalate”, polyethylene terephthalate - Wiktionary, the free dictionary , otherwise found in pop bottles.

It's in the title. PET, or as ruffles pointed out, polyethylene. I believe the thin roll up cutting boards found at Target are polyethylene, and the thickness is about right.

For high heat applications I use Kapton sheet (not cheap) . For low heat I use the covers from $1/3pk of small spiral bound writing notepad’s I found at the dollar store.