Dear Jim: I am tired of old leaky inefficient windows that stick closed or won’t stay open and sweat during the winter. What is the very best type of replacement windows that are maintenance-free and long-lasting? – Carl A.

Dear Carl: Replacement (or for new construction) windows with fiberglass frames are clearly the best type of windows available. If I had to replace the windows in my own home, I would definitely choose fiberglass windows. As homeowners become aware of the advantages of fiberglass, they are becoming more popular.

Maintenance-free fiberglass windows cost more than some vinyl windows, but are priced similar to high-quality wood and clad windows.

Factoring in their maintenance-free life and long-term high energy-efficiency, fiberglass windows have one of the lowest lifetime costs of any frame material.

Other than metal, a heat conductor, fiberglass is the strongest frame material. This allows the frame profile to be narrow for more glass area to provide a better outdoor view and more natural light indoors. Its strength allows much larger custom windows to be produced than with most other frame materials.

Most fiberglass windows are made by a pultrusion process which is different from the way boat hulls and Corvette bodies are produced. Long glass fibers are coated with a resin. They are pulled through a hot die with the shape of the window frame profile. The heat cures the resin to form a strong frame member.

This thermosetting resin cures chemically, so it will no longer melt or weaken substantially from high heat. In contrast, vinyl is a thermoplastic material that loses strength when heated. This is why dark frame colors, which get hot in the summer sun, are acceptable with fiberglass.

In addition to strength, the long glass fibers in the fiberglass frames expand and contract with temperature changes at the same rate as the glass window panes. This makes the glass and frame perform as a single unit, minimizing stress and wear on the seals and allowing many manufacturers to offer lifetime warranties.

Fiberglass windows can be painted at the factory with several decorator colors or you can paint them at your house for a perfect match. For an elegant look, choose fiberglass windows with natural real oak wood interior veneers and snap-off grilles for easy cleaning. They are held on by hidden clips.

Fiberglass windows are tops in energy efficiency. Some fiberglass window frames offer optional foam insulation filling (up to R-10). With triple-pane, low-e glass and krypton gas fill, the glass panes are also R-10 in the center.

Since fiberglass windows, like vinyl ones, are made to custom fit your window openings, they are fairly easy to install yourself for big savings.

Write for (instantly download – www.dulley.com) Update Bulletin No. 567 – buyer’s guide of 10 high-quality fiberglass window manufacturers listing styles, glass options, frame colors, features and typical installation instructions. Include $3 and a business-size SASE, and send to James Dulley, 6906 Royalgreen Drive, Cincinnati, OH 45244.