Question

Why wooler cloth keep us warm

Answer 1

Wollen cloths have small air pockets that act an an insulator. Heat produced by our body will not be able to easily escape due to the air pocket insulation and thus our body heat is trapped inside an keeps us warm. Similarly, the outside cold air was not able to penetrate the wollen cloths very easily.

Answer 2

The main reason that woollen clothes are able to keep us warm is, that they have tiny holes (pores) between them.

We know that Air is bad conductor of heat. Hence, these traps actually traps the air inside the body and don't allow the heat from inside to escape outside.