Even well fitting doors and windows can allow some air movement. These narrow gaps can be sealed by draught excluders and weatherseals.
Draught excluders are flexible foam or rubber strips held in place by rigid wood and metal strips which are screwed or nailed to the edge of the door or window.
Weatherseals are lightweight stick-on strips, available in a variety of profiles, e.g. "U" shaped gaskets can be cut to slip over the lip of window frames, and flat strips can be attached to the inside, sealing the edges of door or window frames. Open cell foam strips are not as durable as closed cell strips.
When stick-on products are used, good surface preparation is essential. Usually this involves cleaning the surfaces well with methylated spirits.