Tweed, once it has been woven, is not cloth until it has been washed and pressed.
Nowadays tweed is finished by specialist companies with the necessary equipment to wash, dry, press and brush cloths. The finishing of cloths is a very important part of the process. Without this, threads would not cling together to provide stability and warmth, and the fabric would easily fray and disintegrate.
In this film on Facebook, a group of women in the Western Isles waulk the cloth. The wet fabric is pummelled to soften and shrink it, accompanied by songs, like the one in the YouTube clip below, to keep the rhythm going and spirits up during what would have been quite a tedious (not to mention smelly) process otherwise!