By David Russell, reporter at OptionMonsterNEW YORK -- Option traders made a killing in Dow Chemical ( DOW) on Friday, riding a wave of bullish sentiment in the materials sector. OptionMonster's tracking programs detected heavy volume in the September 39 calls, with large blocks pricing early for $0.33 to $0.43. The chemical stock was up about 1% when the first trades hit. These calls lock in the price where shares can be purchased, letting investors position for potential gains while controlling the amount of capital at risk. Given their relative inexpensive cost, the contracts can generate significant leverage relative to the underlying stock. That's exactly what happened on Friday. Dow's shares continued to advance, ending the session up 3.06% to $38.04, and those calls roughly doubled to $0.83 in the process. (See our Education section) The company is the third-biggest holding in the SPDR Materials Fund, which was the only major sector exchange-traded fund to close the session higher. Materials also rallied on Thursday after strong Chinese trade numbers suggested that economic activity is quickening in the world's most populous country. Overall option volume was 13 times greater than average in Dow, with calls outnumbering puts by a bullish 7-to-1 ratio. Russell has no positions in DOW.