Updated September 2026. Specifications from Pella documentation. How we research products
Pella 250 Series
- Manufacturer
- Pella
- Material
- Vinyl, multichambered frame, welded sash
- Positioning
- Mainstream vinyl, below Impervia
- Warranty
- Lifetime non-glass for the owner-occupant; 10 transferable years on sale
Pella Impervia
- Manufacturer
- Pella
- Material
- Duracast fiberglass; special shapes in fiberglass-resin
- Positioning
- Pella’s fiberglass line, above the 250
- Warranty
- Lifetime on Duracast for the owner; special shapes 10 transferable years
Main difference: the same manufacturer in two materials. Vinyl against Duracast fiberglass, with narrower frames and powder-coat dark colors on the Impervia side and a lower price territory on the 250 side. Both lifetime headlines convert to 10 transferable years on sale and carry two years of labor. Illustrations are UpgradeWorth drawings, not product photographs. No winner is declared.
UpgradeWorth has not physically tested either product. This comparison is built from Pella’s own product pages, its warranty documents and dealer material, with the source named beside anything that is not from Pella.
This is the upgrade conversation that happens in most Pella showrooms: the vinyl line, or the fiberglass one. Same manufacturer, same installer, same glass options. The honest answer is that the material difference is real, and it is worth paying for in three specific situations and not in the rest.
Side by side
| Pella 250 Series | Pella Impervia | |
|---|---|---|
| Frame material | Vinyl, multichambered frame with welded sash; optional foam-filled frame | Pella's proprietary fiberglass, which Pella calls Duracast: a thermoset, five-layer material. Pella states it has displayed superior strength over wood, vinyl, aluminum and wood-plastic composites in tensile and three-point bend tests to ASTM D638 and D790, and that it expands and contracts at close to the same rate as glass |
| Styles | Awning, casement, double-hung, single-hung, sliding, picture, bifold, bay and bow, as listed on Pella's own 250 Series page | Double-hung, casement, awning, sliding and picture windows plus special shapes, as listed in Pella's Impervia shop; patio doors are also offered in the line. Special shapes are made from a fiberglass-resin material rather than Duracast, which matters for the warranty |
| U-factor | Not published as a single range by Pella. NFRC-certified values are published per style and glazing option in Pella's Architectural Design Manual. A Pella dealer page cites U-factors as low as 0.27 for the configurations it sells | Not published by Pella as a single range. NFRC-certified values are published per style and glazing option in Pella's technical documentation. A Pella dealer page cites 0.27 for a configuration it sells |
| SHGC | Not published as a single range by Pella. A Pella dealer page cites SHGC as low as 0.21. Check the NFRC label of the exact unit quoted | Not published by Pella as a single range. Dealer-cited 0.21 for one configuration. Check the NFRC label of the exact unit quoted |
| ENERGY STAR | Pella states the line offers options that meet or exceed ENERGY STAR certification in all 50 states | Pella states Impervia products with dual-pane glass offer energy-efficient options that meet or exceed ENERGY STAR guidelines in all 50 states |
| Warranty | Per Pella's vinyl window and patio door limited warranty: non-glass materials and workmanship carry a Limited Lifetime Warranty for the original purchaser in an owner-occupied single-family home; on transfer of ownership, or when the buyer stops occupying the home, it is replaced by a transferable 10-year limited warranty; labor is included only within two years of the date of sale; laminated glass carries a transferable 10-year term. Read the current written warranty before purchase | Per Pella's Impervia limited warranty: a non-transferable Limited Lifetime Warranty on the Duracast material that makes up the frame and rectangular sash parts, against cracking, splitting, corroding and warping, for as long as you own the home; labor included only within two years of the date of sale; on transfer of ownership, or when the buyer stops occupying the home, a transferable 10-year limited warranty replaces it. Special-shape products made from fiberglass-resin carry a transferable 10-year term on non-glass materials. Read the current written warranty before purchase |
| Price position | Not publicly specified | Not publicly specified |
| Installation | Insert and full-frame replacement; also sold through the Pella at Lowe's program | Replacement and new construction; sold through Pella showrooms, the Pella Pro dealer network and the Pella at Lowe's program |
Specifications from each manufacturer. Empty fields mean the value is not publicly specified, not that it is zero.
The material difference
The 250 Series is vinyl on a multichambered frame with a welded sash. Impervia is Pella’s proprietary fiberglass, which it calls Duracast: a thermoset, five-layer material. Pella states it has outperformed wood, vinyl, aluminum and wood-plastic composites in tensile and three-point bend tests carried out to ASTM D638 and D790, and that it expands and contracts at almost the same rate as glass.
That last point is the technical heart of the argument. A frame that moves at the same rate as the glass it holds stresses the seal less over decades of temperature cycling, which is the mechanism behind most failed insulated glass units. These are manufacturer tests with manufacturer framing, and no independent field study we could find settles how much difference it makes in a real wall over twenty years.
The warranty difference nobody points out
Both lines carry a Limited Lifetime headline, and both convert to a transferable 10-year term when you sell the house or stop living in it. Labor is included only within two years of the sale on both.
The detail worth knowing is inside Impervia: the Limited Lifetime coverage applies to the Duracast material used in rectangular products. Special-shape windows in the line are made from a fiberglass-resin material instead, and carry a transferable 10-year term on non-glass materials. If your project includes arched or shaped units, that is a different warranty on the same order form, and no salesperson has ever volunteered it in our reading of the documents.
Sightlines and glass area
A stronger material allows narrower frames for the same opening, which is why Impervia is marketed on sleek profiles and more glass. On a small bathroom window that difference is negligible. On a wall of large units it is visible, and it is the aesthetic reason people pay the premium rather than the thermal one.
Colors
Impervia uses a factory powder-coat finish meeting AAMA 624, in five colors, with dual-color frames pairing a white interior with Brown, Tan, Morning Sky Gray or Black exteriors. Dark exteriors are exactly where vinyl draws the most objections, so if black is on your list, this is the line that answers it within Pella’s range.
Energy performance
Pella states that both lines offer configurations meeting or exceeding ENERGY STAR in all 50 states. Neither publishes a single U-factor range, because certification follows the glass package. One dealer cites 0.27 with 0.21 SHGC for both an Impervia configuration and a 250 Series configuration it sells.
Read that carefully: at the configurations that dealer quotes, the two lines land in the same place. If a salesperson tells you fiberglass is dramatically more efficient than vinyl, ask to see the two NFRC labels side by side. The glass package moves this number far more than the frame does.
Price
Pella publishes no installed prices. What exists as market evidence: regional installers quote roughly $500 to $900 per window installed for the 250 Series, and our published fiberglass territory runs $1,100 to $2,200 per window installed. On a fifteen-window house that gap is a five-figure decision, so it deserves the same scrutiny as the windows themselves.
Put your own numbers through the cost calculator, and if you already have both quoted, compare the two quotes before assuming the difference is the material.
Consider Impervia when
- Your climate runs to sustained extremes of heat or cold
- You want dark exteriors, or a powder-coat finish rather than through-color vinyl
- The openings are large and you want the slimmest frames and the most glass
- You intend to stay in the house for decades
- You are replacing a handful of windows, where the premium is hundreds rather than thousands
Consider the 250 Series when
- You are doing the whole house and the budget is the binding constraint
- Your climate is moderate
- You expect to move within about ten years
- Standard sizes and white or neutral exteriors
- You would rather spend the difference on a better glass package and a better installer
What we could not compare
Neither line publishes a like-for-like U-factor range, visible transmittance, or installed pricing, so those rows say so rather than being filled by estimate. We have not tested either product and we publish no satisfaction ratings, because we have no data that would support one.
Sources
- Pella Impervia product pages and Pella Pro Dealer Impervia page
- Pella 250 Series product page
- Pella vinyl limited warranty (PDF) and the Pella Impervia limited warranty document