Abstract: A thermal break in a metal (e.g. aluminum) frame window or door is characterized by two spaced metal sections joined together by an insulative block of poured and hardened thermal fill material which projects inward toward the sash at least to the same extent as the inward-most-projection of the metal sections in the break region. One or more surfaces of the block may serve as a guide for a sliding sash. This construction eliminates the metal conductive path, from outside to inside, which extends along inward-most portions of the jamb in prior art windows. Preferably, the thermal breaks in the jamb and sill are co-planar to provide a continuous thermal break around the entire frame. The method of forming the block of thermal fill utilizes at least one mold surface to which the fill material does not adhere during hardening so that the block can be easily removed from the mold.