in the UK during official play, and boots are recommended for all play everywhere. The UK also recommends goggles, elbow pads and gum shields. A shirt or jersey is required that distinguishes the player's team, and is not black and white stripes like an umpire shirt. White polo pants or trousers are worn during official play. Polo gloves are commonly worn to protect from working the reins and mallet. Not permitted is any equipment that may harm horses, such as certain spurs or whips. Ball The modern outdoor polo ball is made of a high-impact plastic. Historically they have been made of bamboo, leather covered cork, hard rubber, and for many years willow root. Originally the British used a white painted leather covered cricket ball. The regulation outdoor polo ball is to in diameter and weighs to . Plastic balls were introduced in the 1970s. They are less prone to breakage and much cheaper. The indoor and arena polo ball is leather-covered and inflated, and is about in diameter. It must be not less than or more than in circumference. The weight must be not less than or more than . In a bounce test from on concrete at , the rebound should be a minimum of and a maximum of at the inflation rate specified by the manufacturer. This provides for a hard and lively ball. Mallet The polo mallet consists of a cane shaft with a rubber-wrapped grip, a webbed thong, called a sling, for wrapping around the thumb, and a wooden cigar-shaped head. The shaft is made of manau-cane (not bamboo, which is hollow) although a small number of mallets today are made from composite materials. Composite materials are usually not preferred by top players because the shaft of composite mallets can't absorb vibrations as well as traditional cane mallets. The mallet head is generally made from a hardwood called tipa, approximately 9" inches long. The mallet head weighs from to , depending on player preference and the type of wood used, and the shaft can vary in weight and flexibility depending on the player's preference. The weight of the mallet head is of important consideration for the more seasoned players. Female players often use lighter mallets than male players. For some polo players, the length of the mallet depends on the size of the horse: the taller the horse, the longer the mallet. However, some players