I have made a decent heat pump, with 4 x peltier elements each at 48W. Each element will be switched with a separate relay. I will later install DS18B20 sensors in the heatsinks, embedded in thermal paste. Right now my problem is to choose the best, most workable insulation material. It will be placed as a thermal barrier between the hot and cold chambers, which each have their own airflow running.

Here is the datesheet of ds18b20

I chose PU-foam, which is popularly used for e.g. water heaters. The label says it is a cancer risk, so I was wondering what you lot would recommend as an alternative. PU-foam will harden, and make it impossible to remove my pump for repairs etc.

What's the best practice here?