Pella Windows
Plastic jamb liners come with some Pella Architect Series windows. A plasticky vinyl jamb liner is present on the Style Edition (SE) model of windows. Architect-series windows are made with aluminum-clad wood. Double-hung windows have a a distinct design, made with a horizontal muntin that splits the window into sections (usually two, but sometimes additional muntins are in place to create more sections).
Window Replacement
Some jamb liner material may be present even after you remove old windows from the frame. The jamb liner is designed to press right up against the frame, creating an airtight seal, and may stay behind when you remove the rest of the window. First, search for frame attachment fasteners that may be integrated into the jamb liner. Remove these fasteners before removing the jamb liner. Spring-loaded balances located inside jamb liners can be tricky to remove; they may pop out at you as you work. Use care when removing old windows, and move with precision to avoid injury.
Window Finishing
Plastic jamb liners on Pella double-hung windows provide insulation and weatherproofing as well as create a snug fit between window and frame. Do not get paint, stain or finish on the jamb liner when you are finishing your windows. Clean away any finishing materials that accidentally get on the jamb liner immediately to avoid compromising the integrity of the insulation that's integrated into the liner. You should also avoid getting finishing materials on the sash edges; this may cause the sash to stick to the jamb liners.
Repairing Jamb Liners
If the spring-loaded balance cartridge inside a plastic jamb liner ruptures or breaks prior to installation, you must repair it before you may install your Pella double-hung windows. Take apart the broken cartridge and locking mechanism, then place a new cartridge and mechanism inside the jamb liner. The pulley mechanism must be restrung for the spring-loaded mechanism to work. You may order replacement parts directly from Pella.