As an HALS light stabilizer supplier who’s spent the better part of a decade troubleshooting polymer weathering issues for construction product manufacturers, this is one of the most common questions I get at trade shows, over Zoom calls, and on follow-up emails after a first demo: Can HALS light stabilizer be used in building materials? HALS Light Stabilizer
The short answer is yes—though it’s not a one-size-fits-all yes, and there’s a lot of nuance that most spec writers, product engineers, even general polymer suppliers skip when first explaining HALS to construction teams. I’ve seen builders reject HALS out of hand because they confused it with older UV inhibitors, I’ve seen structural engineers overcompensate and overuse it to the point it caused more problems, and I’ve watched a small prefabricated siding company save $120k a year in warranty claims by switching from a generic UV additive to a properly formulated HALS system. Let’s break this down like I would over a cup of coffee at a construction supply conference—no overly jargon-heavy explanations, just the real-world stuff I’ve learned helping 70+ building material brands adjust their formulas over the years.
First, let’s ground this in what building materials actually face, because that’s the whole point here. A vinyl window that sits on the east side of a 10-story office in Phoenix isn’t dealing with the same conditions as a PVC fence in coastal Florida, or a polycarbonate greenhouse panel in the Pacific Northwest. Each of those materials is exposed to a different mix of UV intensity, heat, humidity, salt air, even pollution—all things that break down polymers over time. When a polymer breaks down, it doesn’t just look faded. It becomes brittle. It cracks. It loses structural strength. For building materials, that’s not a cosmetic issue—that’s a safety, warranty, and brand reputation issue.
Let’s start with what HALS actually does, because that’s where the confusion starts. HALS stands for Hindered Amine Light Stabilizer. I know, it sounds like a random chemical acronym, but if you think of it as a repair crew for polymer degradation, it makes sense. UV radiation from the sun hits a polymer chain, breaks a molecular bond, creating what’s called a free radical. That free radical starts a chain reaction: it breaks another bond, creates another free radical, and so on, until the polymer becomes brittle and fails. Older UV inhibitors worked by absorbing that UV radiation before it could hit the polymer, but they get used up pretty quickly—within 2-5 years of sun exposure, usually, which is why so many vinyl fences fade and crack right around their 3rd year. HALS doesn’t absorb UV light. It captures those free radicals mid-reaction, neutralizes them, and breaks the chain before it can cause damage. And the best part? HALS doesn’t get used up as fast. It’s a catalytic stabilizer, meaning it keeps working for 10, 15, even 20 years if formulated right.
Now, why was there ever a question about whether HALS works in building materials? The early HALS products, from the 1970s through the early 2000s, had a bad reputation. They were low molecular weight, which meant they migrated to the surface of the polymer too fast—causing a foggy residue that made plastic look cloudy, or even staining porous materials like wood-plastic composites (WPCs). Some also reacted with other common additives in building materials, like carbon black (used to make black vinyl siding) or acid scavengers, breaking down before they could do their job. That left a lot of construction teams with a bad taste in their mouth for HALS, and they stuck with older benzophenone or benzotriazole UV inhibitors, or even skipped UV additives entirely for projects they considered “low-exposure.”
But here’s the thing: the HALS products we manufacture and supply today are a totally different animal. Modern HALS are high molecular weight, non-migrating, and formulated to work specifically with the additives construction materials use. Let’s run through the most common building materials that we’ve successfully helped apply HALS to, because that’s the practical stuff you care about if you’re a spec writer, product engineer, or building owner:
First, vinyl siding and window profiles. This is the biggest use case for HALS in building materials, and for good reason. Vinyl (PVC) is cheap, durable, and lightweight, but it’s notoriously prone to UV degradation. I worked with a major North American siding brand a few years back that was getting 20-25 warranty claims a year for siding panels that cracked and turned brittle after 7 years in the Texas sun. They were using a generic benzotriazole UV inhibitor, and when we switched their formula to a HALS system specifically calibrated for PVC (they paired it with a small amount of a UV absorber for the first 3 years, to give the HALS time to build up its protective layer), their warranty claims dropped to 1 claim in 5 years. The key here was matching the HALS type to the material: low molecular weight HALS works great for thin, fast-curing products, but PVC siding is 40-60 mils thick, so a mid-molecular weight HALS that doesn’t migrate too fast is perfect.
Next, wood-plastic composites (WPCs) for decking, railing, and trim. WPCs are a mix of wood flour and plastic, so they have the same UV degradation issues as plastic, plus they’re porous—meaning any surface residue from old HALS products would soak into the wood fiber and cause staining. That’s why early HALS was bad for WPCs, but today’s non-migrating HALS, often called “non-blooming” HALS, sit inside the polymer matrix where they belong, so they don’t stain. We also worked with a WPC decking manufacturer last year that was having trouble with their gray line of decking fading unevenly after 2 years in coastal North Carolina. They were using a standard HALS, but it was reacting with the UV brighteners they added to make the gray color pop. We switched them to a specialized HALS formulated for colored WPCs, and their color retention is now at 90% after 3 years, which is way above the industry average of 75%.
Then there are polycarbonate and acrylic glazing panels, like those used for greenhouses, skylights, and patio covers. These materials are see-through, so they can’t have any haze or discoloration from stabilizers—another reason old HALS was a no-go. But modern transparent HALS are designed to not affect the clarity of polycarbonate, and they hold up much better than UV absorbers. A greenhouse manufacturer in the Netherlands I work with has used our transparent HALS for their polycarbonate panels for 8 years, and the panels still transmit 92% of visible light (almost no haze) while resisting UV degradation, compared to their old UV absorber system which was at 85% light transmission after 5 years. The added bonus? The HALS also protects against heat aging, which is a big deal for skylights that get 120°F in the summer.
Now, I need to be honest here—HALS isn’t right for every building material, and it’s not a magic fix. Here’s where spec writers and engineers get tripped up, and where I spend the most time advising:
First, HALS doesn’t work on its own for materials that get extreme UV exposure. For example, a vinyl fence in Arizona, which gets up to 10x more UV than a location in the Pacific Northwest, will still need a small amount of a primary UV absorber paired with HALS. The HALS takes care of the long-term degradation, and the UV absorber takes care of the short-term high-intensity UV. It’s a synergistic system, not a replacement. Using HALS alone in high-UV areas will work, but the material will start to fade after 10 years instead of 20, which can negate the long-term cost benefit.
Second, some materials have inherent properties that make HALS less effective, or require specialized formulation. For example, materials with high levels of acid scavengers, like polyethylene pipes, can react with some HALS types, rendering them useless. In those cases, we work with the manufacturer to test a specialized, non-reactive HALS that’s calibrated for their specific additive package. Another example: materials used for ground contact, like plastic deck supports or foundation wraps, are less exposed to UV, so HALS is usually unnecessary there—you’d just use a basic UV inhibitor if needed, since the long-term UV protection isn’t a priority.
Third, there’s the cost factor. HALS is slightly more expensive per pound than generic UV inhibitors, but the long-term savings on warranty claims, product replacement, and brand reputation make it a no-brainer for most exterior building materials. Let’s do a quick math example: a siding panel costs $12 to manufacture, and has a 20-year warranty. Using a $0.10 per pound UV inhibitor leads to $0.30 in warranty costs per panel over 20 years, while using a $0.18 per pound HALS leads to $0.05 in warranty costs per panel. That’s a net gain of $0.07 per panel, and that adds up fast when you’re making 100,000 panels a year. I’ve had clients tell me that the switch to HALS paid for itself in warranty savings in 12 to 18 months.
Another common question I get: Will HALS affect fire resistance, or other performance properties that building materials require? For most common building materials, no. We’ve done testing with UL standards for vinyl siding fire resistance, and adding properly formulated HALS doesn’t change the flame spread rating or smoke development index. For materials that have strict fire codes, like insulation or roofing underlayment, we test every HALS batch to make sure it doesn’t interfere with fire retardant additives. We also work with clients to adjust their formulations if needed—sometimes you can reduce the amount of fire retardant a tiny bit when adding HALS, since the polymer degradation is slower, but we always recommend full third-party testing for code compliance.
Let’s also talk about the future, because this is a space that’s changing fast with the push for more sustainable building materials. A lot of construction teams are moving to recycled polymers now, since recycled PVC, PE, and PP are cheaper and more eco-friendly, but they’re also more prone to degradation because they’ve already been weathered once. HALS is perfect for recycled materials, because it protects the new polymer matrix from UV and heat damage, extending the life of the recycled material by 5-10 years. We recently worked with a company making 100% recycled plastic landscape timbers, and adding our HALS allowed them to offer a 15-year warranty instead of the 5-year warranty they had to offer before, because their product would crack and turn brittle. That’s a big deal for sustainability—extending the life of recycled materials means less waste going to landfills, and less need for virgin plastic.
Now, I know what some of you are thinking: I’ve heard that HALS can cause blooming, or staining, or affect the color of pigments. That’s a valid concern, especially for colored building materials. But modern HALS formulations solve almost all of those issues. The key is choosing a HALS that’s matched to your pigment and polymer type. For example, if you’re making a white vinyl siding, you want a HALS that doesn’t interact with titanium dioxide (the pigment used for white). For black siding, you need a HALS that doesn’t react with carbon black. We have a library of formulations we’ve tested over the years, so we can tell a client in 5 minutes which HALS will work for their specific product, no guesswork.
I want to wrap this up with a real example, because that’s what sticks. A few years ago, I was at a building products expo, and I met a guy who owned a small prefabricated home company in Florida. He was complaining that his vinyl windows were cracking after 6 years, and he was getting so many warranty calls that he was about to raise his home prices by 10% just to cover the costs. I asked him what stabilizer he was using, and he said a generic UV inhibitor from a big chemical supplier that he’d used for years because it was cheap. I sent him a sample of our mid-molecular weight HALS, and told him to test it on a small batch of windows. Three months later, he emailed me: the windows were still looking new, no fading, no cracking, and he’d cut his warranty claims by 90%. He switched his entire window line to our HALS, and told me that the small increase in material cost was more than offset by the fact that he could keep his home prices competitive, and he’d actually had more sales because he could offer a 15-year window warranty instead of 5.
So, to circle back to the original question: Yes, HALS light stabilizer can absolutely be used in building materials. It’s not a one-size-fits-all solution, it requires matching the HALS type to your specific polymer, pigment, and exposure conditions, and it’s not always the cheapest option upfront. But for exterior building materials that need to last 10, 15, 20 years—vinyl siding, windows, WPC decking, glazing panels, recycled plastic products—HALS is one of the most effective, cost-efficient, and long-lasting stabilizers on the market.
If you’re a spec writer, product engineer, or building material manufacturer who’s dealing with UV degradation, fading, or warranty claims, and you want to see if HALS is right for your products, we can work with you to test small batches, adjust your formulations, and make sure you get the performance you need without compromising on code compliance, color, or fire resistance. Reach out, and we can walk through your specific project or product together.
HALS Light Stabilizer References:
- Lam, F. L., & Scott, G. (1997). Polymer Photodegradation and Photostabilization. Chapman & Hall.
- Klemchuk, P. P. (2000). Handbook of Polymer Degradation and Stabilization. CRC Press.
- American Society for Testing and Materials (ASTM) Standard G154, Practice for Operating Fluorescent Ultraviolet (UV) Lamp Apparatus for Exposure of Nonmetallic Materials.
- National Fire Protection Association (NFPA) 70, National Electrical Code, Article 352 (Rigid Nonmetallic Conduit).
- Plastics Europe. (2022). Weathering Performance of Exterior Construction Plastics: A Supplier’s Guide to Stabilization Solutions.
Jinan Tonex Chemical Co., Ltd.
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