Fulling is the process of shrinking and thickening woollen cloth after it has been woven.  This makes the cloth more hard wearing. Fulling is performed by pounding the newly woven cloth in an alkaline liquor.  It was the first textile process to be mechanised. The first reference to a fulling mill in Gloucestershire dates back to the 12th century.  The alternative to mechanised fulling was treading the cloth with bare feet in some form of container.   This had all but died out this century so this is a very rare picture showing the cloth, the tubs and the 'walkers'.  

A similar effect may be experienced when knitted socks are worn for an extended time in wellington boots.   It is often found that the heels of the socks become 'felted' so that the individual stitches become indistinguishable from one another.  The surnames Fuller, Walker and Tucker all derive from the fulling process