I would like to make my own insulated coat for a kettle (or whatever else I can think of). There are commercially available products for this like the brewcoat.com and that's basically the look I'm going for. the brewcoat says it uses "3 mm thick polyester felt and polyester polar". to me it looks like the stuff you use for speaker carpet which apparently has thermal stability properties and is used for a wide variety of applications. that's probably the outside layer but I'm not sure what the inside layer would be, it looks like the same stuff just lighter in colour. Gagne wrote a blog about the brewcoat a while back and he adds some aerogel material to increase the insulation properties. So maybe a homemade one could be this speaker carpet as the outside layer and aerogel as the inside layer stitched together. Does anyone have suggestions on what material would work well (or not work well)?

yup, if you want a good, cheap option, consider oven mitt material, available at any fabric store. Insul Brite is one of the brand names, then you can cover that with whatever you want. It's cheap and easy to work with.