Weather stripping is the placement of sealing materials around windows and doors to keep out rain, snow, or cold air. You'll find weather-stripping materials in the form of self-stick tapes and nail-on strips. The self-stick versiona come in rubber, foam, or vinyl. For metal and vinyl windows that can't be nailed into, self-stick weather stripping is the only choice. Look for EPDM rubber weather-stripping (EPDM is a kind of synthetic rubber), as it lasts the longest. High-density foam tape is also a good choice, but open-cell foam tape won't stand up to the elements for long. Vinyl V-strips also wear out quickly. For wooden windows, nail-on strips are best. Use spring bronze weather strips that are nailed in place and spring open to close air gaps.
Applying self-stick weather stripping
For double-hung windows, start by cleaning the jambs, the bottom edge of the sash (where it meets the sill), and the back of the bottom sash with a solution of mild dish detergent and water. Rinse and let dry. The adhesive material won't stick to a gritty or dorty surface.
Starting with the sash bottom, cut the self-stick weather stripping of your choice to length and peel back the adhesive tape. Keep a straight line in affixing the weather stripping to the bottom edge. Next, you'll do the sides, or jambs. With the bottom sash raised all the way up, cut two lengths of weather stripping and work it between the sash and the jamb. Finally, cut some weather stripping for the top edge of the sash. Raise the sash up 3 to 4 inches and press the strip firmly onto the back of the sash so that it's even with the top edge.
For casement windows, open the window and clean the edges with a solution of mild dish detergent and water. Once all the surfaces are dry, cut the self-stick weather stripping to length, peel back the tape, and press it onto the jambs and sill where the window makes contact.
Applying nail-on weather stripping
If you have wood windows, and want to weather-strip with a material that's long lasting and has some archietctural character to boot, spend the extra dough for spring bronze weather stripping. The spring in these bronze strips compresses so that when the window closes, a weathertight seal is created. This type of weather stripping lasts longer than foam types, but the isntallation is a little more laborious.
Spring bronze atrips come in different widths, so make sure you measure your sashes and jambs before purchasing. Use tin snips to cut the strips to length. You'll secure them to all the moving or operational parts of the window. (If it's a double-hung window, you'll attach it around all four sides, and the top rail of the bottom sash.) Ideally the strips have small holes you'll nail into. If not, sinking the tiny heads on the tiny nails, or brads, is persnickety and time consuming.