Why does a lump of cotton and wool shrink in water?

A lump of cotton and wool shrinks in water due to the absorption of moisture. Both materials are made of natural fibers that can absorb water, causing them to swell and alter their structure. When the fibers absorb water, they can become saturated and lose some of their original shape, leading to a perceived shrinkage as the fibers contract during drying or upon release of moisture. Additionally, the heat from washing or drying can further cause fibers to tighten, contributing to the shrinking effect.