system
Given the following post, respond as if you're commenting on Reddit:
human
If I have two blankets of different materials, does the total insulation change depending on how I layer them?

for instance, I have a cotton sheet and a polyester blanket.

Would having one on top trap heat more effectively than the other way around?
gpt
Thermal mass can have an impact if there are changes in temperature involved. Having the denser layer on the inside keeps the temperature more constant.

NZ's building code, for example, requires that new buildings built with concrete blocks have them within the insulation layer, not outside.

Other effects that could have an impact are wind and water. Many types of insulation get significantly less effective if full of water, and also perform better without airflow, e.g. glass-wool batts.