Although many choose wood window frames for aesthetic and even health reasons (as wood has been proven to be a calming influence on people), some wood frames offer superior thermal performance because many species of wood are natural insulators. Wooden frame carpenters typically glue several layers of wood together with durable glues for strength and stability. The grain of each of the pieces (laminations) of wood is parallel to the frame. Wood conducts less heat across the grain than along it.

Wood’s natural insulating property is enhanced by addition of layers of superior insulating materials such as cork, dense wood fiber, and others, but wood covers these layers so that they are hidden when the window is installed.

Wood may be durable in many climates, but in some climates, especially rainy climates, owners must periodically apply a finish to the outside of the frames to protect the wood. These surface treatments close and seal the surface so that the porous wood will not absorb moisture. Similar sealants may be applied to the surface of the wood frame facing indoors to protect it from stains, condensing moisture, and soiling. Most of these sealants include substances to block UV radiation which can discolor the wood. Untreated, the wood may bleaching or darken.

Some manufacturers offer wood frames with the outside of the frame covered by vinyl or metal to protect the wood.