Insulation is equally effective in keeping heat out of the tent on very hot days and at keeping it in during cold days or nights. Keep in mind, the point of insulation is not to actually produce heat itself, but rather prevent the passing of heat through it - more of a barrier. Think about the insulation in a house. The house does not supply heat or cold air (A/C), but the insulation in the house keeps you warmer inside in the winter and cooler in the summer.
When it's cold outside, you produce the heat inside (through body heat or portable heating solution) and the insulation is the barrier that helps prevent that heat from getting out. When it's hot outside, the insulation is the barrier that helps keep the heat out and if you have a portable fan or A/C, the insulation will help trap that cool air. Our insulation has a thermal conductivity of 0.03 W/(m.K), which is excellent to keep the proper temperature inside the tent. You can see more in our cold weather test here: