(HDPE) and ultra-high molecular weight polyethylene (UHMW) are the only materials that offer reasonable skating characteristics, with UHMW synthetic rinks offering the most ice-like skating but also being the most expensive. A typical synthetic rink will consist of many panels of thin surface material assembled on top of a sturdy, level and smooth sub-floor (anything from concrete to wood or even dirt or grass) to create a large skating area. Operation Periodically after the ice has been used, it is resurfaced using a machine called an ice resurfacer (sometimes colloquially referred to as a Zamboni – referring to a major manufacturer of such machinery). For curling, the surface is 'pebbled' by allowing loose drops of cold water to fall onto the ice and freeze into rounded peaks. Between events, especially if the arena is being used without need for the ice surface, it is either covered with a heavily insulated floor or melted by allowing the fluid in the pipes below the ice to warm. A highly specialized form of rink is used for speed skating; this is a large oval (or ring) much like an athletic track. Because of their limited use, speed skating ovals are far less common than hockey or curling rinks. Those skilled at preparing arena ice are often in demand for major events where ice quality is critical. The popularity of the sport of hockey in Canada has led its icemakers to be particularly sought after. One such team of professionals was responsible for placing a loonie coin under center ice at the 2002 Winter Olympics in Salt Lake City, Utah; as both Canadian teams (men's and women's) won their respective hockey gold medals, the coin was christened "lucky" and is now in the possession of the Hockey Hall of Fame after having been retrieved from beneath the ice. Standard rink sizes Bandy In bandy, the size of the playing field is x . For internationals, the size must not be smaller than . The variety rink bandy is played on ice hockey rinks. Figure skating The size of figure skating rinks can be quite variable, but the International Skating Union prefers Olympic-sized rinks for figure skating competitions, particularly for major events. These are . The ISU specifies that competition rinks must not be larger than this and not smaller than . Ice hockey Although there is a great deal of variation in the dimensions