Dow Corning Silicone Sealant 789 vs Polyethylene: A Buyer’s Honest Comparison

The Mistake That Made Me Write This

I've been handling industrial supply orders for about nine years. I'm not an engineer — I just sign the purchase orders and deal with the consequences. In that time, I've personally documented seven material-related mistakes that added up to roughly $23,000 in wasted budget. The one that hurt most happened in 2019, and it started with me trying to save about $200.

A contractor asked for Dow Corning silicone sealant 789 for a parking structure. I looked at the price and decided a polyethylene-based sealant would be good enough. It was half the cost. The order had to go before end of day, so I didn't push back or ask for a sample. I put the purchase through.

Six months later, the sealant had cracked and peeled away from the concrete. We spent four days grinding it out and reapplying silicone. The total extra cost was around $1,500 — plus a one-week delay and a very annoyed contractor. Honestly, polyethylene sealant isn't a common shelf category. I think what I got was a polyolefin-based product sold as a low-cost alternative. Whatever the exact chemistry, it wasn't silicone, and that was the point.

How I Compare Polyethylene vs Silicone Now

When someone asks me to compare polyethylene and silicone, I don't just look at the price per cartridge. I look at four things:

• Weather resistance
• Flexibility and recovery
• Adhesion
• Total cost over time

If a material fails on the first three, the fourth doesn't save you. That's the lesson I had to learn with a $4.20 tube of sealant.

Weather Resistance: Silicone Stays Flexible

Architectural silicone is formulated for outdoor exposure. Dow Corning 789 is a neutral-cure silicone that stays flexible across a broad temperature range — roughly -40°C to 150°C — and handles UV exposure far better than most thermoplastics.

Polyethylene, on the other hand, is a semi-crystalline thermoplastic. It gets more brittle in cold weather and can degrade over time in direct sunlight. I saw that happen not just with the failed sealant, but also with a set of polyethylene wheel stops at a loading dock in 2021. The first winter cracked one right at the anchor hole.

Full disclosure: I wasn't thinking about polymer chemistry when I bought those wheel stops. They looked like rubber, and they were cheap. I learned the hard way that appearance isn't a specification.

If you're buying rubber wheel stoppers, the material debate that matters is usually polyurethane (TPU) vs rubber, not polyethylene vs silicone. TPU and rubber have the impact resistance and abrasion resistance you want under a wheel. Polyethylene doesn't. Since then, I've worked with a TPU supplier who makes heavy-duty wheel stops, and the difference in material quality was obvious from the first sample.

Flexibility and Recovery: The Elastic Memory Test

A sealant has to move with the joint. Silicone elastomers have excellent elastic memory. After a joint expands and contracts, a good silicone sealant returns to its original shape. That's why products like Dow Corning silicone sealant 789 are specified for expansion joints and glazing.

Polyethylene isn't an elastomer. It deforms. In a moving joint, that creates stress at the bondline and leads to cracking or delamination.

I learned this a second time when I tested a high-flex polyethylene sealant on a small job. The spec sheet looked great. Three months later, the first cracks showed at every corner. That experiment cost about $890 in material and labor, plus a week of delay.

Adhesion: Polyethylene Doesn't Like to Stick

Polyethylene has very low surface energy. Gluing it, painting it, or sealing it is notoriously difficult. If a product is billed as a polyethylene sealant, I'd ask how it actually bonds to concrete or metal. Often, the answer is not very well.

Silicone, by contrast, bonds well to most building materials — glass, aluminum, steel, masonry. That's why architectural silicones are such a practical choice for exterior sealing. I'm not saying you can skip surface preparation or primer rules. But silicone is a much more forgiving material for this kind of work.

The Cost Question: Cheap Is Expensive

Let me give you a real breakdown from my failed 2019 project.

• 32 cartridges of PE-based sealant: about $134
• Labor to apply: about $650
• Labor to remove failed sealant and reapply silicone: about $1,720

Total outlay: about $2,500. If I had bought silicone from the start, the material would have cost about $380, and the total with labor would have been around $1,000. My smart purchase ended up costing about $1,500 extra and a week of delay.

As of early 2025, Dow Corning silicone sealant 789 is still priced higher upfront — roughly $10–14 per cartridge at typical distributor pricing, depending on color and quantity. A generic PE-based sealant might cost $4–6. The difference feels significant at the moment of purchase. It's not.

Honestly, I'm not sure why the distributor didn't question my order for an outdoor concrete joint. My best guess is they assumed I knew what I was doing. I didn't. That's why I now ask more questions.

So What Should You Buy?

Here's my honest, practical take:

• Outdoor sealant on moving joints (concrete, glass, metal, masonry): choose a real architectural silicone like Dow Corning silicone sealant 789. The upfront price is worth it.
• Rubber wheel stoppers: don't go with polyethylene or silicone. Talk to a TPU supplier or a rubber fabricator about polyurethane and rubber options.
• Indoor, static, non-critical applications: polyethylene might be acceptable. I'm not going to pretend it's always the wrong material.

If you're in the indoor static 20%, maybe the cheaper option is fine. If you're in the 80% of cases involving outdoor exposure or joint movement, silicone is probably the no-brainer.

The Surprising Part About This Comparison

Here's the thing that caught me by surprise: polyethylene and silicone are rarely competing for the same job. They're different tools.

Polyethylene is a thermoplastic used in packaging, pipes, bottles, and some products like wheel stops. Silicone is an elastomer used for sealing, gasketing, and other flexible applications. Saying polyethylene vs silicone is a bit like comparing a water bottle to a rubber band. Both are useful, but you wouldn't pick between them without knowing the application.

So if you're searching for polyethylene vs silicone because you're choosing a material for rubber wheel stoppers, you're probably asking the wrong question. The real choice is usually between TPU and rubber. A good TPU supplier can explain the trade-offs in durometer, abrasion resistance, and cold-weather performance much better than I can.

Limitations and Fine Print

I'm a procurement person, not a materials engineer. New formulations of polyethylene and other polyolefins come out every year. If you have a specific application and a product data sheet that says it will work, test it. Don't write off an entire material category based on one mistake.

Also, this comparison is based on my experience with building sealants. For structural or life-safety applications, always consult a licensed engineer and follow the manufacturer's technical data sheets.

Product classification references ASTM C920, which covers performance requirements for building sealants. Dow Corning 789 is an example of a neutral-cure architectural silicone used in glazing and facade joints. Pricing quotes are from January 2025; verify current rates before budgeting.

Bottom Line

If you're choosing between polyethylene and silicone for an outdoor sealing job, I'd pick silicone almost every time. Dow Corning silicone sealant 789 is the specific product I wish I had ordered in 2019. It might cost more at the register, but it saves money over the life of the project.

But don't stop at the material comparison. Think about the actual product. If you need rubber wheel stoppers, polyethylene is not my pick, and silicone isn't either. Reach out to a TPU supplier for polyurethane or rubber options. Match the material to the job — that's the real lesson.