GRP actually stands for Glass Reinforced Plastics, the reinforcement is principally to improve strength and impacts very little the fire properties. Although GRP can refer to almost all materials, it is often associated with thermosets such as Unsaturated Polyesters or Phenolics. These materials are often used in fire critical applications such as boats, aeroplanes and railway carriages and subways. The properties of materials can be altered and enhanced through the inclusion of Flame Retardant additives and coatings and therefore it is difficult to generalise. Specifications for products often lay down the required fire performance and hence this information is available for most compounds semi finished products. Further details on Plastics Materials can be found on this website in the How to Process Plastics section.