Since the start of the 2007 season, F1 had a sole tyre supplier. From 2007 to 2010, this was Bridgestone, but 2011 saw the reintroduction of Pirelli into the sport, following the departure of Bridgestone. Seven compounds of F1 tyre exist; 5 are dry weather compounds (labeled C1 through C5) while 2 are wet compounds (intermediates for damp surfaces with no standing water and full wets for surfaces with standing water). Three of the dry weather compounds (generally a harder and softer compound) are brought to each race, plus both wet weather compounds. The harder tyres are more durable but give less grip, and the softer tyres the opposite. In 2009, the slick tyres returned as a part of revisions to the rules for the 2009 season; slicks have no grooves and give up to 18% more contact with the track. In the Bridgestone years, a green band on the sidewall of the softer compound was painted to allow spectators to distinguish which tyre a driver is on. Beginning in 2019, Pirelli scrapped the tyre naming system such that the tyres will denote at each Grand Prix independently as hard, medium and soft with white, yellow and red sidewalls respectively rather than having a separate name and colour for each of the five tyres. The change was implemented so that casual fans could better understand the tyre system. Generally, the three dry compounds brought to the track are of consecutive specifications.