The difference between fiberglass and steel doors is the skin: both are two thin faces over a foam core, usually 1 3/4 inches thick in all, and the faces are either molded fiberglass or sheet steel. In ProVia’s 2024 catalog its Signet fiberglass door rates a U-factor as low as 0.16 against 0.17 for its Legacy steel door, and steel costs less.
We install both, fiberglass entry doors and steel entry doors, in homes from St. Louis out to St. Charles County. Where the door hangs decides it: fiberglass for a stained or sunny door, steel for a painted, sheltered one or the door from the garage.
Side by Side
| Fiberglass | Steel | |
|---|---|---|
| Skin | molded fiberglass | sheet steel, 20 gauge |
| Wood look | convincing up close, takes stain | reads as wood from the street |
| Dents | resists them | dents, and they stay |
| Rust | cannot rust | where a scratch breaks the coating |
| U-factor | 0.16 (Signet) | 0.17 (Legacy) |
| Finish warranty | 15 years (Signet), 10 (Ascent) | 10 years (Legacy) |
| Stains | 20 plus 7 glazes (Signet), 7 (Ascent) | 7 (Legacy) |
| Price | higher | lower |
| Pick it for | stained front doors, full sun | painted doors, garage entry |
Styles for each are on our fiberglass page and steel page.
What Is a Fiberglass Door?
A fiberglass door is an entry door made of two molded fiberglass skins over a core of insulating foam, with a frame of stiles and rails around the edge. The skin is molded with a wood grain deep enough to take a real stain.
As of September 2026, ProVia’s site lists two fiberglass doors: Signet, with skins in Cherry, Mahogany, Oak, Knotty Alder, Fir or Smooth, and the newer Ascent, in White Oak or Smooth. Its older Heritage and Embarq doors no longer appear there.
ProVia’s Signet page shows hardwood stiles and rails dovetailed and glued at each corner, and its 2024 catalog shows a composite bottom rail to resist rot. Its Ascent page lists wood stiles on both sides, a polyurethane core and closed-cell foam spacers in the bottom corners to keep water out.
What Is a Steel Door?
A steel door is an entry door with two steel skins over a foam core. ProVia’s Legacy uses 20 gauge steel, which ProVia says is 49% more steel than a 24 gauge door. Gauge runs backward, so the lower number is the thicker skin. Our steel entry door guide explains each gauge.
ProVia’s 2024 catalog says the steel is hot-dipped galvannealed, with 300% more coating thickness than electro-galvanized steel, which is why sound steel does not rust.
Which One Insulates Better?
Fiberglass, but by less than most comparisons suggest. U-factor measures how fast heat passes through the whole door, frame included, and lower is better.
ProVia’s 2024 catalog lists the Signet and Legacy slabs at 1 3/4 inches with a foam core, so the skin decides little of the heat loss. The seals, the frame and the glass decide most of it, and on both doors ProVia uses a bulb and blade sweep, CornerShield weatherstripping and a Z-AC threshold with an auto-adjusting riser.
A door with a full lite of glass loses more heat than a solid one, whatever the skin. ProVia’s 2024 catalog adds a Low-E pane to Legacy doors with a full or half lite of decorative glass so they can qualify for Energy Star. ProVia’s site lists Energy Star options for Signet, Ascent and Legacy. So compare the U-factor for the exact door and glass on each quote, not the brochure’s lowest.
Which One Is More Secure?
Steel, a little, and less than people think. A kick-in rarely punches through the face of a door, because what gives first is the jamb where the bolt sits. That is why ProVia’s 2024 catalog lists a 20 gauge steel security plate and an adjustable brass strike plate on both Signet and Legacy. Each gets three ball bearing hinges, and an 8 foot door gets four.
The same catalog gives Signet a 4 1/4 inch hardwood strike stile behind the lock and a 2 5/8 inch hinge stile, and every ProVia steel door a composite lock block.
Dents, Rust and Sun
Steel dents. A ladder, a bike pedal or hail can leave a mark. ProVia says a dent in its Legacy can be filled with an auto body repair kit, which works but still shows on smooth paint. The same knock does not dent fiberglass.
Steel rusts only where a scratch cuts through the paint and the galvanneal under it. Touch those up the week you find them.
On a west wall in a St. Louis July, dark steel gets too hot to hold a hand on. Fiberglass takes the heat better, but a stain still fades sooner on a door with no porch over it. ProVia’s 2024 catalog credits Signet’s longer finish warranty to its DuraFuse finishing system, and says every finish warranty can be shorter in extreme exposure.
Which Looks More Like Wood?
Fiberglass, up close: standing at the door, it passes for wood. ProVia’s Legacy steel comes with a woodgrain texture that takes a stain, like the pair above, and from the sidewalk it reads as wood.
If you plan to paint, smooth painted steel and smooth painted fiberglass look the same from anywhere, and ProVia’s site lists the same 33 paint colors for Signet, Ascent and Legacy. It also says each of the three can be ordered with one look outside and another inside. Our fiberglass entry door guide shows more of the stained looks.
How to Tell Which Door You Have
You can check this yourself in a minute. Hold a fridge magnet flat on the face of the door: it sticks to steel and slides off fiberglass.
Do not go by the edge. Plenty of steel slabs have a wood edge, and ProVia’s Signet page shows a wood edge on that fiberglass door too, so wood there proves nothing.
Faded fiberglass can often be refinished. Steel rusting through along the bottom usually needs replacing.
Which One for Which Door
When I price a door, the first thing I ask is which way it faces, because sun and weather can rule out a material before taste comes into it.
- A front door you want stained. Fiberglass.
- A front door you will paint, with a porch over it. Steel. Painted and sheltered, the two look alike and steel costs less.
- A door in full afternoon sun. Fiberglass, or steel in a light color.
- A busy door with kids, dogs and a stroller. Fiberglass, because it does not dent.
- The door between the garage and the house. Steel. Section R302.5.1 of the International Residential Code, 2021 and 2024 editions, accepts a solid or honeycomb core steel door or a solid wood door there, at least 1 3/8 inches thick. Fiberglass qualifies only with a 20 minute fire rating. The door must latch by itself and have a self-closing or automatic-closing device, and no door may open from the garage straight into a bedroom. Your city’s adopted code has the last word, so check the label.
What About Wood?
Real wood has real grain, but in full sun it needs refinishing far more often than fiberglass or steel. Our types of exterior doors guide compares all three.
What Moves the Price
For the same size and style, steel costs less, and after the skin these move the number:
- Glass. Sidelites, a transom and decorative glass can cost more than the door.
- The finish. A factory stain costs more than paint, and ProVia’s 2024 catalog says every Signet ships finished.
- The frame. A composite frame costs more than wood and will not rot. ProVia’s 2024 catalog offers its PermaTech composite frame with a lifetime limited warranty, or a FrameSaver wood frame with a composite bottom.
- The hardware. A handleset and deadbolt range widely, and ProVia’s 2024 catalog requires multi-point hardware on an 8 foot Signet.
- The whole unit or just the slab. A new frame with the door costs more and fixes more.
When a New Door Is Not the Answer
If the door is sound and the draft comes from worn weatherstripping or sweep, you do not need a new door. Replace the seals first. If the frame has rotted at the bottom, a new slab in the old frame will not fix it, and the frame has to go too. If you are pricing an overhead garage door, that is a different trade: we install entry, patio and storm doors.
Common Questions
Picking Yours
Tell whoever prices it three things: which way the door faces, whether you want to stain or paint it, and how much glass you want. ProVia’s door brochures show every style, and ProVia’s site says all three doors come in custom widths and heights in 1/8 inch steps. The 2024 entry door catalog holds the U-factors, gauges and parts cited above.
We are a ProVia Platinum dealer and a Certified Installer of Entry Doors, and ProVia’s dealer locator is the place to confirm both. ProVia’s site says its doors carry a lifetime limited warranty, and that it transfers once, to the next owner of the home. ProVia’s 2024 catalog applies that term to the slab, jamb and glass on Signet and Legacy, breakage included. Our own work is guaranteed for 10 years. You can see doors we have hung in our gallery. Browse all the doors we install, ask for an estimate, or call 314-277-5952 with those three answers ready.
