Yellowing, warping, loss of airtightness, sagging sashes, air leaks... If you're thinking about buying PVC windows, you've probably heard about these problems. They come up in forums, in conversations with neighbours, and even among some industry professionals.
Is there any truth to them? Yes, there was. 60 years ago.
As professional installers with over 15 years of experience, we've seen it all: PVC windows that look perfect after 30 years and windows that turn yellow after just 3. The difference isn't the material — it's the quality of the profile and its formulation. And in 2026, there are specific reasons why some of these problems are reappearing.
In this article, we tell you the full story: where these problems came from, how they were solved, and why you should pay attention to certain details before buying.
The early years: when PVC really did cause problems (1954-1970)
The first PVC window in history was manufactured in 1954 in Germany. It was created by a metalworker named Heinz Pasche, at the Dynamit Nobel factory in Troisdorf. It was a steel frame coated in soft PVC — a flexible plastic that, in theory, would protect the metal from corrosion.
The problem appeared quickly: soft PVC expanded and softened in direct sunlight. In summer, the frames warped. Literally.
Additionally, the earliest PVC formulations used stabilisers that seem unthinkable today:
- Cadmium: A heavy metal and carcinogen used as a heat stabiliser. It prevented PVC from degrading during manufacturing, but was highly toxic.
- Lead: Used as a whitener and stabiliser. Effective and cheap, but toxic and polluting.
With these ingredients, it's no wonder PVC earned a bad reputation. The windows did yellow, did warp, and did contain hazardous substances. But that was over half a century ago.
How the problems were solved: from soft PVC to high-tech PVC
The industry didn't stand still. During the 1960s and 70s, advances were made that completely transformed the material:
The switch to rigid PVC (Hart-PVC)
The first major leap was replacing soft (plasticised) PVC with rigid PVC without plasticisers — what we now know as PVC-U (U for "unplasticised"). This PVC didn't soften in heat and maintained its shape for decades.
Titanium dioxide (TiO₂): the invisible protector
In the 1960s, manufacturers began incorporating titanium dioxide into the PVC formulation. This white compound acts as a sunscreen for plastic: it absorbs ultraviolet radiation and prevents the molecular structure of PVC from degrading.
Thanks to TiO₂, profile lifespan went from a few years to over 40 years without significant changes in colour or mechanical properties.
The elimination of toxic substances
The European Union progressively eliminated hazardous stabilisers:
- 2001: Cadmium banned in PVC profiles in the EU (voluntarily by manufacturers)
- 2015: Lead banned across the EU-28
Today, quality profiles use calcium-zinc (CaZn) stabilisers — harmless, effective and recyclable. Brands like Kömmerling market it under the name "Greenline" technology.
PVC in 2026 has nothing to do with PVC from 1960. It's like comparing a modern car with one from the 1950s: the base material is the same, but the engineering is completely different.
Galvanised steel reinforcement: the skeleton nobody sees
There's a fundamental component of PVC windows that goes completely unnoticed: the internal galvanised steel reinforcement.
PVC, by its nature, is a relatively soft material (it has a low elastic modulus). On its own, it doesn't have enough rigidity to withstand wind pressure, the weight of glass, or thermal expansion. That's why a galvanised steel profile is inserted inside the main chamber of each profile, acting as a skeleton:
- Provides structural rigidity against wind
- Maintains dimensional stability when temperature rises
- Improves airtightness (a more rigid window = better seal)
- Is essential for large windows
A little-known fact: steel reinforcement has 3 times more rigidity than aluminium of the same thickness. That's why PVC windows with steel reinforcement are used even in Passive House buildings, the most demanding in the world for energy efficiency.
Why is this important to know? Because some manufacturers, to cut costs, reduce the reinforcement or replace it with fibreglass or rigid foam. These alternatives may work in small windows and mild climates, but they haven't been proven in areas of high solar radiation like Spain. Without adequate reinforcement, the window loses rigidity in heat — and that's when problems with closing, leaking and warping begin.
PVC climate zones: why they exist and what they mean
When German manufacturers started exporting their profiles to southern European countries — Spain, Italy, Greece — they encountered an unexpected problem: the same profiles that lasted 40 years in Germany degraded much faster in the Mediterranean.
The reason was solar radiation. In Munich, annual solar radiation on a horizontal surface is about 4.5 GJ/m². In Barcelona, it exceeds 5.5 GJ/m². In Seville, over 6.0 GJ/m². That difference is devastating for a plastic material exposed outdoors for decades.
Manufacturers understood they needed to adapt the PVC formulation according to the destination climate. In 2003, this idea was formalised in the European standard EN 12608, which classifies profiles into two zones:
- Zone S (Severe): For countries with solar radiation ≥ 5 GJ/m²/year. Requires more titanium dioxide and a formulation more resistant to UV rays. All of Spain, Italy and Greece are Zone S.
- Zone M (Moderate): For countries with solar radiation < 5 GJ/m²/year. Allows a formulation with less TiO₂, more economical. Germany, Poland and Romania are Zone M.
The difference between a Zone S and Zone M profile is invisible to the naked eye. Both are white, both look identical. The difference is in the internal chemical composition — and it shows after 3-5 years of installation, when the Zone M profile in a Zone S climate starts to yellow and lose properties.
Manufacturer warranties: what they really cover
Premium manufacturers offer 10-year warranties on their profiles:
| Manufacturer | Profile warranty | Note |
|---|---|---|
| VEKA | 10 years | RAL certified (German quality mark since 1984) |
| Kömmerling | 10 years | Greenline technology (lead-free since 2004) |
| REHAU | 10 years | — |
| Salamander | 10 years | — |
| Cortizo | 10 years | Spanish manufacturer — all production is Zone S |
But there's a fine print that very few people know about: these warranties are only valid if the profile corresponds to the correct climate zone. If a Zone M profile is installed in Spain, the manufacturer's warranty doesn't cover the problems that may arise, because the product has been used outside its specifications.
And if the profile comes from a parallel import (purchased outside the manufacturer's official channel), it simply has no warranty coverage.
Why past problems are returning in 2026
This is where the story becomes worrying. The problems that the industry solved decades ago — yellowing, warping, degradation — are reappearing in Spain.
The cause has a name: parallel imports of PVC profiles from Eastern Europe.
What's happening exactly?
- Profiles purchased in Poland and Romania at prices well below the official channel
- These profiles are manufactured with Zone M formulation (for moderate climates)
- They are sold and installed in Spain, which is Zone S (severe climate)
- In some cases, they have insufficient or non-existent steel reinforcement
- The result: the same symptoms that windows had in the 1960s
It's a technical regression. PVC isn't a bad material — it's being used with a formulation designed for a different climate. It's like putting summer tyres on a car that will drive through mountains in winter: the tyre isn't bad, it's simply not the right one.
Why is it legal?
Because the EN 12608 standard classifies profiles, but doesn't prohibit selling Zone M in a Zone S country. The Spanish Building Technical Code (CTE) regulates the thermal transmittance of the complete window, but not the climate classification of the individual profile. It's a legal loophole that parallel imports exploit.
How to detect an inadequate profile
- Ask the installer for the profile certificate with the EN 12608 classification
- Check that the letter "S" appears (for Severe Zone)
- Ask if the profile comes from the manufacturer's official channel (with warranty valid in Spain)
- Be wary of prices significantly below market — the difference is usually in the formulation
What to demand when buying PVC windows in 2026
If you're considering changing your windows, these are the key points to verify:
- Zone S profile: Ask to see the EN 12608 classification. All of Spain is Zone S.
- Class A (per EN 12608): Profile outer walls ≥ 2.8mm. Class B (≥ 2.5mm) is inferior.
- Galvanised steel reinforcement: Ask if the profile has steel reinforcement and what thickness. Essential for large windows.
- Manufacturer's official channel: Make sure the manufacturer's warranty is valid in Spain.
- Lead-free stabilisers: All serious European manufacturers already use calcium-zinc, but it doesn't hurt to verify.
- Professional installer: The best window in the world, badly installed, doesn't work. Look for installers with proven experience.
If you want to know exactly how much it would cost to change your windows with certified profiles, use our online price calculator or request a quote with no obligation.
Frequently asked questions about PVC window problems
Do PVC windows yellow over time?
Quality PVC windows, with Zone S formulation and sufficient titanium dioxide, do not yellow under normal conditions. Those that may yellow are profiles with cold-climate formulation (Zone M) installed in areas of high solar radiation like Spain.
Do PVC windows warp in the sun?
Modern PVC (rigid, with galvanised steel reinforcement) is designed to withstand thermal expansion without warping. However, a profile without adequate reinforcement or with Zone M formulation in a Zone S climate may suffer warping under sustained high temperatures.
Is PVC toxic?
Modern PVC no longer contains cadmium (banned in the EU since 2001) or lead (banned since 2015). Current stabilisers are calcium-zinc, completely safe.
How long do PVC windows last?
With a quality profile (Zone S, Class A, steel reinforcement, recognised manufacturer), a PVC window can last over 40 years without losing colour or properties. The German RAL-GZ 716 seal has certified this durability since 1984.
What's the difference between a Zone S and Zone M profile?
The difference is the internal chemical composition: a Zone S profile has more titanium dioxide (UV protection) and a more heat-resistant formulation. Visually they are identical. The difference shows after 3-5 years in sunny climates.
What are parallel imports of PVC profiles?
They are profiles purchased in countries with lower manufacturing costs (Poland, Romania) and resold in Spain outside the manufacturer's official channel. The problem is they usually have Zone M formulation (for cold climates) and don't carry a valid warranty for the Spanish market.
How do I know if my windows have a Zone S profile?
You can ask the manufacturer or installer for the profile certificate according to EN 12608. The letter "S" must appear in the classification. If they can't provide it, that's a warning sign.
Is Cortizo better than German brands?
Cortizo has a unique advantage in the Spanish market: by manufacturing in Spain, all its production is automatically Zone S. German brands (VEKA, Kömmerling, REHAU) also manufacture Zone S, but you need to verify that the specific profile being installed is actually Zone S and comes from the official channel.
Is it worth paying more for quality PVC windows?
The price difference between an imported Zone M profile and a Zone S from the official channel can be 15-25%. But a window with an inadequate profile may need replacement after 5-8 years, while a quality one lasts over 40. The real cost of "saving" on the profile is much higher in the medium term.
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