Which interior wall material/wall thickness provides good sound insulation?

With a prefabricated house, it would probably look different in winter...

Why is that?

Because there is "kein" or little material that stores heat.

Well, we haven't had any heating in our building for two weeks now and constant 19 degrees at these outside temperatures.

Because there is "no" or little material that stores heat.

Usually significantly better insulation values, so temperature-wise almost nothing happens overnight at first. After days of outage in winter, the situation of course looks different, since - as you wrote - less heat is stored in the house.

We already noticed 2 days in winter at below freezing temperatures during the construction phase. However, we also ventilated and there was no internal entry. Currently, we rather have the problem of getting the temperature below 22°C - shading was already necessary and ventilating in the morning helps (excluding the last 3 days).