uPVC and vinyl share a plastic. The windows are worlds apart.

"Vinyl" and "uPVC" name the same material: rigid PVC with no plasticizer in it. The frame of an American vinyl window is uPVC. So the honest answer to the common objection, that uPVC is just vinyl, is yes, as far as the polymer goes. The difference is in how the window is designed, what is put inside it, and what it has been tested to.

Clearing up the plasticizer story.

It is often said that vinyl contains plasticizers and uPVC does not. That is not right. Flexible PVC, the kind used for cable sheathing and flooring, contains plasticizers. No window frame is made from it. Every PVC window frame, on either side of the Atlantic, is the rigid, unplasticized kind.

The two words come from two markets. "Vinyl window" is the North American term. That product grew up in the house market, around hung windows and sliders, light profiles and quick replacement work. "uPVC window" is the European term. That product grew up around inward-opening casements, heavy glass and compression seals. Same plastic, two different windows.

What actually differs.

The formulation. PVC resin is never used alone. It is blended with stabilizers, impact modifiers, pigment and UV protection. The recipe decides how the profile copes with sun, heat and impact over the years. Recipes differ between producers in both markets, so this is a question to ask, not a point to assume. Profile standards exist in both markets. The European one, EN 12608-1, sorts profiles into classes by wall thickness, impact resistance and climate. The North American one, AAMA 303, sets minimum requirements for impact, weathering, dimensional stability and heat build-up.

The profile. A European-style profile is deeper, with more chambers inside it. The Vistaza Vi5 frame is 70 mm (2-3/4″) deep with five chambers. The Vi6 is 82 mm (3-1/4″) with six. The depth does two jobs. It insulates, and it leaves a glazing pocket deep enough for thick triple glass and laminated acoustic glass. Many residential vinyl frames are designed around double glass.

Steel. The chambers of a European-style profile are shaped to take steel reinforcement. Every Vistaza frame and sash carries a steel core. A residential vinyl window often has little or no reinforcement, because a house-sized window under house-sized wind loads does not need it.

Hardware and seals. A casement sash is pulled against continuous compression gaskets by locking points around its edge. A hung window or a slider has to slide, so it seals with sliding weatherstrip. A sliding seal cannot press as hard as a compression seal. This shows up in air and water results more than any difference in the plastic does.

The classes reached. This is the difference that matters on a drawing. Most residential vinyl windows are rated R or LC under NAFS. That is the right rating for a house. High Performance uPVC windows are tested for commercial classes. The Vistaza Vi6 casement is rated AW-PG100, the Vi5 fixed window AW-PG70 and the Vi5 casement CW-PG50. The letters are explained in what a window's class really tells you.

What does not differ.

Be careful with two claims that are often made.

• Welded corners. Most vinyl windows have fusion-welded corners, just as uPVC windows do. It is not a dividing line.
• Upkeep. Neither needs painting. Neither rots or rusts. Both are cleaned with mild soap and water.

Some vinyl windows are also tested above the residential classes. The name on the brochure does not settle anything. The report does.

Where a vinyl window is the right choice.

• Houses, townhouses and low-rise wood-frame buildings.
• Projects where a hung window or a slider is the style the building calls for.
• Replacement work into existing frames, where an insert window saves the interior finishes.
• Jobs where first cost and a short lead time decide. A local vinyl maker can often deliver sooner than a made-to-order commercial window.

On these jobs a well-made vinyl window with an R or LC rating is doing exactly what it was designed to do.

Where High Performance uPVC belongs.

• Mid-rise buildings, where wind loads and water test pressures rise with height and exposure.
• Specifications that call for CW or AW.
• Larger openings, and heavy glass for sound.
• Tight energy targets that need triple glass in a frame built to carry it.
• Buildings where the owner wants commercial-grade hardware that can be adjusted and serviced.

Do not go by the name. Ask for these.

1. The NAFS class and grade, the report number, and the size that was tested.
2. The NFRC-certified U-factor and SHGC for the exact type and glass, not the best number in the range.
3. Whether the frame and sash are reinforced, and with what.
4. The seal type: compression or sliding.
5. The thickest glass unit the frame can take.
6. The sound test report, if the project has a sound requirement.

The name tells you the polymer. The report tells you the window.

If two windows answer those six questions the same way, they are the same grade of window, whatever they are called. If they do not, the word "vinyl" or "uPVC" was never the point.

See the two series and their ratings on the windows page, or send your plans and we will match a series to each elevation.