Acore Door Company, a division of Kolbe ' Kolbe, now offers fiberglass entry door units. Fiberglass door panels are prehung and the stiles and rails are constructed of composite material, which is waterproof, and will not cup or twist. The high-density core helps to promote energy efficiency and enhance soundproofing. The exterior skin is a combination of raw materials that distribute color uniformly throughout the skin. Acore Fiberglass Door units are offered in a variety of wood grain and smooth panel styles. Fiberglass units can be ordered in five different stained colors and need no further re-finishing or painting.