Question

thick sweaters with large holes are warmer than those knitted with thin wall. why.

Answer 1

Wool is of course an insulator that doesn't allow the heat to escape, but this is also applicable for the thicker woollen sweater which doesn't give warmth as much as the thinner ones. So, a more justifiable answer is that the layer of air between the two thinner sweaters doesn't allow our body heat to escape.