Other single-polymer PSW go through different schemes. Many foams (namely polyurethane, PU) are powdered and grinded to a particle size less than 0.2 mm using two-roll milling, cryogenic grinders or precision knife cutters. Another process used in mechanical recycling is re-bonding, in which recycled foam flakes originating from flexible slab stock foam production waste are usually blown from storage silos into a mixer that consists of a fixed drum with rotating blades or agitators, where the foam flakes are sprayed with an adhesive mixture (Zia et al., 2007). Fig. 4 shows a schematic illustration of the re-bonding process. One of the main advantages of this process is the ability to obtain a clean product with new properties, i.e. higher density and lower hardness.