The physical andmechanical properties of the resin components of FRP systems are infuenced by temperature and degrade at temperatures close to or above their glass-transition temperature  T_g. The T_g for commercially available, ambient temperature-cured FRP systems typically ranges from 140 to 180°F (60 to 82℃). 

The T_g for a particular FRP system can be obtained from the system manufacturer or through testing by dynamic mechanical analysis(DMA) according to ASTME1640.Reported  T_g, values should be accompanied by descriptions of the test configuration, sample preparation, sample curing conditions (time, temperature, and humidity), size, heating rate, and frequency used. The T defined by this method represents the extrapolated onset temperature for the sigmoidal change in the storage modulus observed in going from a hard and brittle state to a soft and rubbery state of the material under test. This transition occurs over a temperature range of approximately 54°F(30°C)centered on the T_g. This change in state will adversely affect the mechanical and bond properties of the cured laminates. In a dry environment, it is generally recommended that the anticipated service temperature of an FRP system not exceed T_g- 27°F (T_g,-15°C), where T_g, is taken as the lowest T_g of the components of the system comprising the load path. This recommendation is for elevated service temperatures such as those found in hot climatic regions or certain industrial environments. In cases where the FRP will be exposed to a moist environment, the wet glass-transition temperature T_gw should be used. Testing may be required to determine the critical service temperature for FRP in other environments.