Why I'm Comparing These Two
I'm the quality manager at a rubber and plastics component manufacturer. I review every incoming material lot and every molded part before it ships—roughly 200 unique items a year. In Q1 2025, I rejected 6% of first-article samples because the Shore A durometer was outside spec. That is the perspective I'm bringing: not a generic which is better, but what to check when you choose between Dow Corning silicone 732 and liquid butyl rubber.
If you search dow-corning on a distributor site, you'll see how many variations exist—sealants, high-consistency rubber, fluorosilicone, liquid silicone rubber. It can be overwhelming. And in my experience, the questions from buyers are usually the same: Will it handle temperature? Will it keep sealing? Will the next batch look like the last one? Those are quality questions, not just material questions.
I'll compare them on five dimensions: temperature, compression set, adhesion, consistency, and compliance. At the end, I'll touch on a related decision—roll insulation vs foam board—because the logic is the same.
1. Temperature and Environmental Resistance
Silicone wins on temperature range. Most dow corning silicone rubber grades, including dow corning silicone 732, hold up from roughly -65°F to 350°F, and some specialty grades go higher. Liquid butyl rubber is usually listed at -40°F to 250°F. That's not a small difference if your joint sits near an engine or a hot lamp.
But butyl has one thing silicone doesn't: very low gas permeability. Put another way, liquid butyl rubber is what you use for inner tubes and vapor barriers because air can't pass through easily. Silicone, by contrast, is more gas permeable. So if you need a gas-tight seal, butyl may still win despite its lower temperature ceiling.
The surprise wasn't the temperature gap. It was how differently the two materials behave outdoors. Silicone handles UV and ozone without much help. Butyl resists weathering too, but it stays soft and tacky, which creates a different set of problems on a production floor. I remember a batch of butyl strips that stuck to the release liner in a way we didn't expect. We had to change packaging, not the material.
2. Compression Set and Sealing Behavior
I'm not a chemist, so I can't speak to the polymer structure at a molecular level. What I can tell you from a quality perspective is how these materials behave in a compressed joint.
Silicone has excellent compression set. You can compress a silicone gasket, hold it for a long time, and when the load is removed it returns close to its original shape—provided you stayed in its service range. That is why silicone rubber is common in door seals, electrical enclosures, and flanged connections.
Liquid butyl does not cure into a rubber network. It stays a viscoelastic mass, so it seals by cold-flowing into gaps. That is an advantage for irregular joints and a disadvantage when you need dimensional stability. Looking back, I should have specified a cold-flow test when we first ordered butyl gaskets. At the time, the datasheet seemed clear enough. It wasn't. A stack of gaskets deformed in storage under their own weight. (Should mention: the vendor replaced them, but we reworked the packaging spec and added a dimensional check after 24 hours.)
This is also the point where silicone novelties come into the picture. Many custom silicone parts—bracelets, phone cases, or industrial covers that get categorized as silicone novelties—use a silicone rubber grade, not liquid butyl, because of this shape-return property. Put another way, if you want it to bounce back, silicone is the safer choice.
3. Adhesion and Chemical Compatibility
Dow Corning silicone 732 is an acetoxy-cure silicone sealant. It bonds to glass, aluminum, steel, and many plastics, and it cures to a flexible rubber. But it releases acetic acid while curing. That means you need to check compatibility with sensitive substrates. I used to assume general purpose meant safe on everything—until a customer saw discolored copper contacts near a 732 joint. Now every new substrate gets a small adhesion and corrosion test before we approve it.
Liquid butyl rubber is different in a key way: it does not cure. It stays tacky, which helps it seal but does not make it a structural adhesive. The bond is more like a sticky conformable gasket than a real adhesive bond. If you need the sealant to also hold parts together, silicone is usually the right choice.
This gets into application engineering territory, which isn't my expertise. I'd recommend testing on your actual substrate and, if possible, under your actual clamping pressure before committing.
4. Batch-to-Batch Consistency and What You Can Inspect
Here's where the supplier brand matters. We use dow corning silicone rubber in many molded parts because the lot-to-lot consistency makes incoming inspection easier. For 732, we check specific gravity, skin-over time, and durometer after full cure. In the last four years, fewer than 1% of Dow Corning lots missed a specification we were tracking.
Liquid butyl rubber has been more variable in our incoming lots. That might be because our butyl comes from a smaller compounder, not because butyl is inherently inconsistent. My experience is based on about 200 incoming lots—mostly molded gaskets and custom silicone parts, not high-volume automotive production. If you're working with a different supplier or a roofing application, your experience might differ.
What I can tell you is that the inspection method matters more than the datasheet. We pull a random sample from each lot, measure durometer, do a 180-degree bend test, and check dimensions after a heat soak. That catches more problems than a full certificate of analysis.
5. Cost, Compliance, and the Green Trap
If you're comparing cost per pound, liquid butyl rubber is usually less expensive than silicone. But the total cost includes scrap, rework, cleanup, and compliance. A tacky butyl sealant can require release liners and special handling that erase the price gap.
And don't make environmental claims you can't back up. Per FTC guidelines (ftc.gov), claims like eco-friendly or recyclable need substantiation. In 2022, I implemented a verification protocol for all material claims. It slowed down quoting by a day, but it cut rejected first deliveries by 34%. What was best practice in 2020 may not apply in 2025. Five years ago, most customers didn't ask for accelerated aging data on every lot. Now it's table stakes.
So Which Should You Specify?
Choose Dow Corning silicone 732 or a Dow Corning silicone rubber grade when you need wide temperature range, low compression set, predictable cure, and clean processing. It's our default for electrical enclosures, oven gaskets, and custom molded silicone components.
Choose liquid butyl rubber when you need a non-curing, low-gas-permeability sealer for irregular joints or vapor barriers—and when you can tolerate tackiness and cold flow. It is also still a practical choice for first-pass water sealing in construction, where a little cold flow works in your favor.
If you're also weighing roll insulation vs foam board, use the same discipline: define your temperature, moisture, and load requirements first. Roll insulation is easier to cut and fit around pipes and studs; foam board gives you a rigid layer with higher compressive strength and a built-in vapor barrier. One is not universally better, just like silicone isn't universally better than butyl.
Even after we approved a silicone batch for a critical joint, I kept second-guessing. What if the cure was incomplete? The two weeks until our accelerated aging results came back were stressful. That's the job. The data turned out fine, and we released the batch. But the lesson stayed: the material with the better datasheet isn't always the one that survives your process.