Hello all, Maybe this is a simple question. I've done some calculations like this, but for heating in buildings. Now it's different. I have some crystals I must keep cold, at -25ºC. So I will surround them with an insulation material wall. Outside we have atmosphere temperature I want to see which material is better (Rohacell, Styrodur...), I know the thermal conductivity, I know the temperatures, but I don't know the thickness of the wall to reach the -25º. I send a picture to illustrate the problem. I know that on the faces of the wall there is convection and radiation, I think here is the biggest problem. So, my question is how to calculate the thinkness of the wall (it's just one material) Thank you!