The apparent volatile-matter content is the percentage of matter lost on heating, relative to the initial mass, The principle of the method specified is obtaining it by measuring the change in mass of a test specimen when heated in an air-ventilated oven at a specified temperature for a specified length of time. The method is applicable to all unidirectional and multidirectional fibre-reinforced prepregs and all thermosetting-resin matrices. Does not apply to unimpregnated reinforcement fibres.