Ply Gem brings out a new side of homes. The company makes and supplies exterior building materials used in home construction and renovation. Its products -- vinyl siding, aluminum windows and doors, stone veneer, and fencing -- are supplied to home-center retailers, distributors, construction companies, and contractors in North America. Subsidiaries include Variform (vinyl siding), Napco (vinyl and metal exterior siding and trim),  Kroy Building Products (vinyl fencing), and Great Lakes Window (energy-efficient vinyl windows and patio doors). Ply Gem Holdings was founded in 2004 to acquire the Ply Gem brand and related assets from building materials manufacturer Nortek. The company went public in 2013.