FOR the first time this year traders at the Hong Kong Futures Exchange all had something in common: their Santa Claus caps. But 10 minutes after the start of trading they found themselves sweating, and there was a call to replace the woollen caps with paper ones. Perhaps the air-conditioning was not cool enough, or perhaps the traders were overwhelmed by the occasion. More than 50 floor traders followed the Christmas tradition as they squeezed into the trading pit. 'It is too exciting to trade with the caps on - our foreheads are sweating,' one trader shouted. Elsewhere, about 300 traders participated in the fund-raising activity yesterday. The Futures Exchange raised over $70,000 this year, more than double last year's total of $30,000.