Fiberglass windows are stronger than vinyl, insulate better than aluminum, and cost less than solid wood, say manufacturers. Serious Materials’ entry-level fiberglass line, the SeriousWindows 525 Series, features foam-insulated frames and optional wood-clad interiors, and includes several styles of fixed and operable windows with R-values from 4.0 to 5.9. Prices start at $40 per square foot ($53 for wood-clad units). Serious Materials, 800/797-8159,