Felting is a process that takes place after weaving a fabric. It involves soaking the woven fabric in water and a fulling substance like soap or mud and then beating or treading it. The aim of this process is to make the fabric thicker, more dense and therefore warmer and waterproof. It is, however, not so easy to recognise whether or not a fabric was felted deliberately because a garment can get the same matted and felted surface when it is used in normal life through the friction of one piece of cloth onto another. On the other hand, the absence of a felted surface does not necessarily mean that a fabric was not felted. The matted surface can easily break away during excavation and finds processing, leaving a clean and unfelted appearance.
There are only a few textiles that show a felted surface. Several of these seem to have been primarily felted. The piled weaves (see 4.4), which were probably used as cloaks, must have been felted. These thick and dense fabrics were clearly meant to be waterproof and a felted fabric would greatly enhance the function of this garment. The mitten found in Dorestad (fig. 21), a thick mantle-like fabric from Dokkum and two pieces from Middelburg are also likely to have been felted. In the case of the Middelburg textiles, it has been suggested that they have a raised nap (Leene 1964). The technique of raising a nap involved roughening up the surface of the fabric with teasels and afterwards shearing the surface back with large iron shears. This technique had been in use since the Roman period (Wild 1970) and is considered a specialist activity in the Early Middle Ages.