Dow Corning Silicone FAQs: What to Know When You Need It Fast

These are the questions I get every time a client is staring down a cutoff and needs silicone yesterday. I've spent 12 years sourcing the stuff for industrial and medical device clients, and I still get tripped up by part numbers. This isn't a complete guide — just the things you need to know, fast. Product info is accurate as of January 2025, but double-check with your distributor before you spec something critical.

• What's the difference between Dow 732 and Dow Corning 732? And what's 99179?
• What is Dow Corning 123 silicone seal used for?
• Can I use Dow Corning silicone to repair a rubber septum?
• Is medical-grade silicone always better than medical grade thermoplastic?
• Is silicone recyclable?
• How do I get Dow Corning products in a rush?
• What do people overlook when they're in a silicone emergency?

1. What's the difference between Dow 732 and Dow Corning 732? And what does 99179 mean?

Short version: no difference. When a spec calls out "Dow Corning silicone dow 732 99179", that's a mashed-together search term for the Dow 732 silicone sealant, usually the 10.3-oz black cartridge, item 99179. The branding just simplified after Dow Corning moved under the Dow umbrella around 2016. But I've seen 99179 listed as white on some supplier sites, and black on others. That's why I always ask for the component and the datasheet before ordering.

The 732 series is a general-purpose RTV silicone sealant per Dow's current product literature. It's fine for gasketing, sealing covers, and light assembly work. It's not a structural adhesive, so don't try to hold anything heavy with it.

2. What is Dow Corning 123 silicone seal used for?

Honestly, I don't have as much hands-on time with Dow Corning 123 as I do with 732, so take this as a starting point: it's a one-part silicone sealant in the Dow Corning lineup, often used for sealing and potting in electronic or small-part applications. I should add that it's not as widely stocked as 732, which means it's rarely available same-day unless your supplier carries it.

The "123 silicone seal" name comes from a legacy drawing number, sort of like how 732 has its own code. If you're speccing it because your company's BOM says "Dow Corning 123 silicone seal", make sure you're also getting the right color, viscosity, and cure behavior. Those variables are easy to miss under a deadline.

3. Can I use Dow Corning silicone to repair a rubber septum?

I get this one a lot from labs. A rubber septum — the little stopper on an autosampler vial — gets punctured and starts to leak. Technically, you can dab just about any silicone sealant on it as a temporary fix, but it's not going to hold pressure or give you a clean seal for long. It's a patch, not a repair.

The right move is to order a replacement septum. Many are made from silicone or butyl rubber, and Dow Corning does make silicone elastomers that could go into molding those parts. But that's a manufacturing job, not something you do with a tube of RTV. If you need a septum that's certified for lab use, don't grab a construction sealant — different material durometer, different extractables, different everything.

4. Is medical-grade silicone always better than medical grade thermoplastic?

No. I'm biased — silicone is my livelihood — but thermoplastics win in a lot of medical device applications. They offer stiffness, clarity, and the ability to be welded or snapped together in complex geometries. Medical-grade silicone is the champion when you need softness, flexibility, and biocompatibility for long-term tissue contact. And there's a difference in manufacturing: silicone often needs molding or extrusion, while thermoplastics give you more options for high-volume injection molding and sterilization.

Medical-grade silicones are often tested against ISO 10993 for biocompatibility; thermoplastics have their own regulatory paths. A specialist who says "silicone can do everything" is an amateur. I'd rather tell you this isn't the right application for our product than let you sink a project into the wrong material.

5. Is silicone recyclable?

Yes, but it's not like recycling a milk jug. Silicone doesn't break down in conventional municipal recycling streams, so it usually ends up in landfill unless you use a specialized program. The good news is there are companies that collect scrap silicone from manufacturing and downcycle it into fillers, insulation, or even new silicone products.

As of my last check (January 2025), dedicated silicone recycling is still a niche, mainly for industrial volumes. If you have a production line generating silicone scrap, you can find recyclers, but expect to pay for transport. For a consumer item like a silicone spatula, you're better off reusing it for years — that's the real sustainability benefit of silicone. It's durable as hell.

6. How do I get Dow Corning products when I have a rush order?

Call your distributor and ask what's on their local shelf — that's the fastest way. Dow 732 is common enough that big distributors usually have inventory. Dow Corning 123 might be special order, which means a 2-day freight is your best bet. I've paid $120 in extra freight before to fly a case of 732 overnight; it saved us from shutting down a production line that was worth $20K an hour. The math was easy.

Also remember: RTV sealants cure by reacting with moisture. According to the Dow 732 datasheet (dow.com), it cures at 1/16-inch per 24 hours at 77°F and 50% relative humidity. If your environment is dry and cold, it'll be slower. If you absolutely must get it operational in four hours, you need a quick-cure product or heat. Don't assume it's cured just because the outside is tacky.

7. What's the one thing people overlook when they're in a silicone emergency?

Shelf life and opened tube condition. A tube of Dow Corning 732 that's been sitting in a drawer since 2019 might look fine, but the cure will be unpredictable. I've been bitten by that exact thing. Looking back, I should have checked the lot number before applying it. Now, every tube in our shop gets a date written on it in Sharpie the day it's opened.

Also keep in mind: one-part RTVs skin over fast at the nozzle tip, but the cure can take days at the core. If you're relying on it for a gasket, wait the full cure time, not just until it feels dry. And if you're cutting it close, build in a buffer, because silicone doesn't care about your deadline.