Low humidity is important during application to prevent cracks from swelling with moisture. Warm temperatures are also necessary so the caulk will set properly and adhere to the surface. Weatherstripping is a narrow piece of metal, vinyl, rubber, felt, or foam that seals the contact area between the fixed and movable sections of a window joint. It should be applied between the sash and the frame, but should not interfere with the operation of the window. The type and quality of the window frame usually affect a window's air infiltration and heat loss characteristics.
Many window frames are available all with varying degrees of energy efficiency.
When properly installed, fixed-pane windows are airtight and inexpensive and can be custom designed for a wide variety of applications. But, because they cannot be opened, fixed-pane windows are unsuitable in places where ventilation is required. Casement, awning, and hopper windows with compression seals are moderately airtight and provide good ventilation when opened. Casement windows open sideways with hand cranks. Awning windows are similar to casement windows except that their hinges are located at the tops of the windows instead of at the sides.