usually very quick where fast, low bounces keep rallies short, and the serve plays a more important role than on other surfaces. Grass courts tend to favour serve-and-volley tennis players. Grass courts were once among the most common tennis surfaces, but are now rare due to high maintenance costs, as they must be watered and mown often, and take a longer time to dry after rain than hard courts. Historically for the Grand Slams grass courts have been used at Wimbledon since 1877, the US Open from 1881 to 1974, and the Australian Open from 1905 to 1987. Hard courts Hard courts are made of uniform rigid material, often covered with an acrylic surface layer to offer greater consistency of bounce than other outdoor surfaces. Hard courts can vary in speed, though they are faster than clay but not as fast as grass courts. The quantity of sand added to the paint can greatly affect the rate at which the ball slows down. The US Open is played on Laykold while the Australian Open is played on GreenSet, both acrylic-topped hard court surfaces. Historically for the Grand Slams hard courts have been used at the US Open since 1978 and the Australian Open since 1988. Carpet courts "Carpet" in tennis means any removable court covering. Indoor arenas store rolls of rubber-backed court surfacing and install it temporarily for tennis events, but they are not in use any more for professional events. A short piled form of artificial turf infilled with sand is used for some outdoor courts, particularly in Asia. Carpet is generally a fast surface, faster than hardcourt, with low bounce. Notable tennis tournaments previously held on carpet courts were the WCT Finals, Paris Masters, U.S. Pro Indoor and Kremlin Cup. Since 2009, their use has been discontinued on the top tier of the ATP. ATP Challenger Tour tournaments such as the Trofeo Città di Brescia still use carpet courts. The WTA Tour's last carpet court event, the International-level Tournoi de Québec, was discontinued after 2018. Indoor courts Some tennis courts are indoors, which allows play regardless of weather conditions and is more comfortable for spectators. Different court surfaces have been used indoors. Hard courts are most common indoors, as they are the easiest to install and maintain. If the installation is permanent, they are constructed on an asphalt or concrete base, as with outdoor courts. Temporary indoor hard