GRP/Composite External Doors from MPN. Your front door is the first impression someone can get from your South Wales home. With a variety of composite range of door styles. GRP Composite Doors from MPN strong secure and locking. Our latest range of luxury double rebated composite doors from MPN. Meridian high-performance composite entrance doors locking system and our composite doors are also thick, 70mm to be precise and GRP skinned, that’s 50% thicker