It Started With a Simple Order
Back in March 2021, I was sourcing sealing strips for a batch of industrial enclosures. The client wanted something that could hold a magnetic door closure, so I naturally ordered magnetic rubber strips — the standard black EPDM with a magnet embedded. I'd used them for years. What could go wrong?
I placed an order for 2,000 linear feet from a familiar supplier. Price was $1.20 per foot. Total: $2,400. I thought, "Good deal. Quick turnaround."
Fast forward two weeks. The strips arrived, I shipped them to the client. Three days later: complaint. The magnet was too weak to hold the door shut in their vibrating environment. Worse, after a week in direct sunlight, the rubber surface started cracking. $2,400 down the drain — plus $800 in rush replacement costs and a 5-day delay.
The Second Mistake: Polyethylene vs Polystyrene
After that disaster, I got conservative. I switched to rigid plastic strips — polyethylene and polystyrene profiles — thinking they'd be more durable. I ordered sample strips from three vendors. The polyethylene ones were flexible but didn't hold a magnet well; the polystyrene ones were brittle and snapped during installation testing. That batch cost $650 for 500 units. We threw away 400 of them.
To be fair, the plastic strips would work fine in a stationary indoor application. But our clients were using these enclosures in outdoor, high-vibration equipment. It was a mismatch from the start. I just didn't know what I didn't know.
The Turning Point: Seeing Silicone Side-by-Side
Then my colleague — let's call him Mark — came back from a trade show with a sample of Dow Corning silicone white extrusion. It looked... plain. White, slightly tacky. He said, "Just try it."
I tested it against the rubber magnet strip. Same thickness, same cross-section. But the silicone had a different feel — more "grip," less "bounce." I clamped them both onto a vibrating test rig we improvised. The rubber strip slipped after 300 cycles. The silicone stayed put for over 2,000. That's when I started paying attention.
Actually, I should mention: the silicone sample was specifically Dow Corning 737 silicone neutro — a neutral cure sealant that comes in cartridges. It's designed for bonding, not extrusion. But the white extrusion we tested was a different product — a solid silicone profile. I got confused at first because of the "737" label on the package.
Learning the Dow Corning Product Family
Once I started researching, I realized silicone products from Dow are not just one thing. There's an entire range:
- Silicone rubbers for extrusion and molding (like the white profile I tested)
- Silicone sealants such as Dow Corning 737 (neutral cure, low odor, good for bonding)
- Silicone fluids used as lubricants or release agents
- Silicone emulsions for textile coatings
- And specialty grades for medical devices, food contact, etc.
But my immediate need was a replacement for the failed rubber magnet strips. I contacted a Dow distributor and asked for recommendations. They sent me technical datasheets for two options:
- A silicone magnetic strip (solid silicone with magnetic particles embedded) — but they warned it wouldn't be as strong as the rubber version in sheer hold. However, it would last 5x longer in UV exposure.
- A silicone profile paired with a separate magnetic insert — that gave better control over strength.
We ordered 500 feet of the white silicone profile with a separate magnet channel. Total cost: $1.85 per foot — or rather, $1.95 with the insert. Installed them on the same enclosure design. Sixteen months later, zero failures. The client actually ordered more.
What I Learned: Industry Has Evolved
It took me three years and about 17 orders to understand that magnetic rubber strips and plastic materials like polyethylene and polystyrene have their place — but they're not universal solutions. The industry has changed. Five years ago, the go-to was cheap EPDM or PVC. As of 2025, high-performance silicone products from Dow Corning offer better resistance to heat, UV, and fatigue. According to Dow's technical literature (Dow.com, accessed January 2025), silicone elastomers maintain flexibility from -60°C to 200°C, while EPDM typically starts degrading above 120°C. That difference matters.
Another thing: don't assume "silicone" means one material. The white extrusion I tested was a different durometer (40 Shore A) than the 737 sealant (a paste, not a solid). I learned to ask for exact product codes and datasheets every time. I now keep a checklist before any material order: temperature range, UV rating, chemical exposure, mechanical stress, and magnet compatibility if needed.
The Takeaway
If you're sourcing sealing solutions and still relying on magnetic rubber strips or basic thermoplastics, you might want to take a fresh look. Not because those materials are bad — they're not. But because the industry has evolved, and what was best practice in 2020 may not be today. At least, that's been my experience across dozens of projects. I've wasted roughly $3,200 over three years learning this. You don't have to.
"Pricing as of February 2025; verify current rates with your Dow distributor. Silicone strip pricing was $1.85/ft when I ordered in Q3 2024. Magnet inserts added $0.10/ft."