The socks are made from a silicone rubber to withstand the heat of the heater block. The underside of the sock is heavily filleted in order to avoid any nooks or crannies into which plastic loves to build up. Together with a fine surface finish which makes this silicone sock very resilient to goop building up on them. For the most part they remain close to spotless with zero build up. Extended printing with very sticky materials can result in some minor build up, however once the hot end cools any material can easily be peeled off the non-stick surface. Keeping the hot parts clean generally makes things much nicer, screws and cartridges can be more easily changed, and nozzles more easily identified.