Coefficient of Thermal Expansion
Large temperature gradients can be detrimental to the gel coat of FRP booms. Major swings in environmental conditions of the boom can lead to cold cracking in the gel coat and in some cases into the resin itself. (See the PDF document linked below for equation.)
WBC booms are made from a fiber reinforced epoxy resin and polyester gel coat. Table 1 in the linked PDF shows the thermal expansion coefficients of both of these base materials. It should be noted that the polyester gel coat is expected to increase over three times more than the fiber reinforced epoxy since the original length and temperature gradient will be constant for both materials. Therefore the coefficient of thermal expansion can be directly compared to represent the difference in the increase of length of the two materials and shows to be 3.5 times larger for polyester than for the reinforced epoxy. The number further skews when fiber orientation is considered.