Why are many layers of clothing often warner than one thick garment ?

Question

Why are many layers of clothing often warner than one thick garment ?

Answer 1

Each layer of air between each layer of clothing traps body heat.

Answer 2

Because each clothing layer traps air underneath it and air is a good insulator.

Same principle that lies behind double glazed windows.

Answer 3

Air is a poor conductor of heat; heat does not pass through it very well. The air trapped between the layers of clothing help "trap" the heat produced by the body.