Fiberglass can look like painted or stained wood, but it isn't as heavy, won't decay, and doesn't dent or rust like steel. Vinyl doors have a stiff foam core that provides good insulation. Design options for either material are limited. Colors are subject to fading, but these doors can be repainted or stained. Good near the seashore, but they may crack in cold weather. Both can be insulated to R-12. Fiberglass starts at $1,500, vinyl at $600.