why does the lump of cotton wool shrink in water Share with your friends Share 0 Riya Gupta answered this Dear Student, A lump of cotton wool shrinks when immersed in water. This is because air present in the cotton wool escapes. Thus, the volume of the cotton wool decreases. Regards 0 View Full Answer Dharineesh Mani answered this Because it absorbs the water very well and due to this it shrinks in water as sponge. 0