Non-Commercial Thermal Insulation I am trying to create a small 10 to 20cm cube that can conserve the heat in 100 to 200ml of 60-90c water in a small Pyrex glass for about an hour. The problem is that I can not use commercial insulators like foam, bubble wrap, and the like. I have searched Google for ideas, but all the results are commercial. I also can not heat or cool the device beforehand, and I have to have a 2cm hole in the top.

I have tried cotton balls and a packed cotton balls with felt mixture, and cotton balls worked the best.
Often the key with stopping the conduction of heat is to provide as many phase transitions as possible. Most thermal insulators achieve this by having voids of Air which is achieved in a variety of ways, bubble wrap, fibre glass etc.

For a "non comercial" I assume they mean stuff you have lying around the lab?

To attempt this I'd layer blue roll / cotton wool / glass wool with tin foil. The more layers the better.