A material that can become very permissible to heat or not, depending on a dynamic configuration.

The first implementation is block that would have many through holes, where thermal insulant or thermal conductive fluid would flow. The more conductive fluid flows, the more it would be permissible to heat. The other variant is a inflatable plastic pouch, where only insulant fluid would flow through. If you pass more fluid the pouch becomes thicker, and the material becomes more heat insulant.

One possible application of this is make house roofs permissible to heat in winter, but not on summer. That could help thermal confort and save energy with air conditioners.