This standard is part of a series of tests for the performance of prepregs, specifying the method for determining the volatile content in prepregs composed of reinforcing materials such as carbon fiber, glass fiber, aramid fiber, and thermosetting resin matrices. The core principle involves heating the sample to drive off volatiles, using an analytical balance with a precision of at least 0.001 g to measure the mass change before and after heating, and expressing the result as a mass fraction. It should be noted that if aramid fiber is used, the absorbed moisture may lead to an overestimation of the results, requiring correction. This method is crucial for controlling the storage stability of prepregs and the quality of composite material products.