Knock, knock Who's there? Therma-Tru. Therma-Tru, who? A part of Fortune Brands Home & Security, that's who. Therma-Tru manufactures fiberglass and steel exterior doors for residential and light commercial use. The company's patio and entry door systems feature wood-grain that resembles mahogany and oak. Smooth-surfaced fiberglass doors that resemble steel are sold under the Smooth-Star brand. Therma-Tru also offers decorative glass and hinges. Its Tru-Defense doors are built to withstand damaging weather and other harsh conditions. All doors are made with polyurethane foam cores for increased insulation. Therma-Tru products are sold in the US and Canada by distributors, lumberyards, and home centers.