INTRO
The honest answer for 70% of Long Island homes is fiberglass. Here's when steel is the better pick anyway.
When to pick steel
Fiberglass wins on the front-facing primary entry door, where curb appeal, stain finish, weatherability, and insulation all matter. On Long Island specifically, the salt air and humidity make fiberglass the longer-lasting choice.
Steel wins on side doors, basement walk-outs, garage-to-house doors, and primary entries where security is the priority and budget is tight.
-- Durability in Long Island weather
Fiberglass does not warp in July humidity, does not shrink in January cold, and does not rot when salt spray hits it. We have never replaced a Therma-Tru fiberglass door we installed in 2011.
Steel is also durable — a Therma-Tru Smooth-Star can last 25–40 years — but it can rust in salt-air environments if paint fails, and it dents if something hits it hard.
-- Insulation
Both fiberglass and steel Therma-Tru doors have polyurethane foam cores that insulate 5× better than a traditional wood slab. The numbers are close enough that energy efficiency is not a meaningful tiebreaker between the two.
-- Cost
Steel is typically 20–30% less expensive than equivalent fiberglass. A standard Therma-Tru Smooth-Star steel entry door runs $1,800–$3,400 installed. A Therma-Tru Fiber-Classic fiberglass runs $2,800–$5,800 installed.
CTA
Still have questions?
This guide was written by James Caruso. If your situation has a wrinkle we did not cover, call us direct. Most questions we answer by phone take five minutes.