Silicone Seal Advice Needed...

I’m trying to seal the housing of a product that has two plastic parts that meet along a straight part line. I’ve looked at competitor products and they all have custom 3D silicone seals, requiring custom moulds and associated $$$.

I can uploads some images if it helps…

I think I can get away with a seal cut from silicone (or similar) sheet and design the sealing activation points/support into the plastic housing…

Is this a bad idea? I’d really appreciate any advice!


Mike, UK

Would an Oring in a tongue and groove not work? I use those on things that need high IP ratings. Could also you an RTV by doesnt allow for clean rework if necessary.

Do you need to do this for mass production, or for a one off?

Molding silicone parts can be done fairly easily and fairly low cost. One off parts can be molded in a DIY fashion but it depends how many pieces you are trying to get out of it.

If you are just trying to do a one off, RTV or caulk might be able to do the trick if you don’t need to ever disassemble it.

Posting your part + your intended quantities and budget is helpful. Sometimes doing it the right way ends up being cheaper in the long run than science projects.

Thanks guys, it’s for 3 initial prototypes, to verify I can seal the unit to IP67 rating…

See image attached, I’m trying to seal the outline below and a tube that will run into the product through the gap visible. An O-seal will work here, just need to think how that interfaces with the two parts and any gaps that might appear. 1m of water will create a fair emount of pressure so everything needs to be well considered…


So if you are trying to design an IP67 seal on that part, I do not see you getting away without a custom seal or custom O-ring.

To build an O ring seal, you need to create a channel around the perimeter of the product (Which will add ~1.5X to your wall thickness dimensions since you will need an inner wall, channel, and outer wall). You then need to create the opposite profile on the other side of the part to compress the O-ring.

You also need to determine how whatever happens on that bottom piece will get sealed, as well as how your screw bosses will get sealed (Ideally you want your screws outside of the sealed area so they don’t create additional entry points).

More important to consider is “What” are you sealing. If you have electronics inside, you may be able to just seal the PCB’s with a simple box enclosure and a square seal vs trying to seal the entire perimeter of the product.

You could also Two shot one of the housings and add an elastomer/TPE shot to one part that creates the seal as part of the housing which then gets crushed on assembly. It makes for 1 more expensive tool, but the cost might be cheaper than creating an additional seal.

Probably a lot of ways to tackle it, but I think either way you’re not going to get away with a simple off the shelf O-ring.

Hi Mike, fantastic idea about a twin shot to achieve the seal! Have never thought of that.

Yes I know all about O-rings from my oil and gas days and the plan would be to use one of them for the tube entering the casing (you can see a rough groove location in the image), some sort of flat silicone seal for the main housing, then its just a tricky case (excuse the pun) of getting the o-ring and silicone gasket to marry up and crush well once the parts are screwed together… Thanks for your help!