Cracks and the gaps between building materials, such as window and door frames, are sealed with caulking and sealant. They are crucial in keeping out pests and preventing water intrusion as well as the seepage of cold air from the outside into a building. Elasticity is the primary difference between sealants and caulking. Although caulking is paintable, it dries more rigidly and is more likely to crack in areas that expand and contract. Sealants work best on surfaces that experience temperature fluctuations, such as the outside of Toronto buildings, and are flexible once dry. They cannot be painted.