For insulating a doghouse against extreme temperatures, wood is the most effective material due to its natural insulating properties, providing a warmer environment in winter and a cooler one in summer. Cedar and pine are excellent choices for their durability and resistance to decay. Additionally, adding insulation panels to the walls, floor, and roof can further enhance temperature regulation. It's crucial to ensure any materials used are non-toxic and safe for pets. Proper insulation, along with strategic placement away from direct elements, will make the doghouse a comfortable retreat for your canine friend.