How's it made? (Silicon brush)

I’m not a pro industrial designer, but I love to know how things are made. Here’s one that seems to be quite a mystery. It’s a silicon brush for cooking. (it’s great for painting melted butter and unlike the standard kitchen brushes this one is possible to clean.)

What’s interesting is that there is only a visible seam on the “back” of the brush where the metal handle enters the rubber. There are no other seams. This doesn’t look like a standard 2 piece injection mold.

Also, look at the long thin bristles. There’s 4 closely packed layers of them, so again this clearly is not injection molding. [EDIT: No, this is wrong. For some reason I was only thinking about the mold cavity being symmetrical. as pointed out below, a cavity just for the bristles would work fine.]

So how is this brush made? Anyone care to guess… or explain :wink: ?


No seams, that sounds interesting. Do you mean he had no parting lines at all. If so how did he remove the part, or was that the idea behind the thesis?

ah yes, a silicon mold can be used for silicon casting. (an old sfx technique isn’t it?)

(OT: silicon does seem to be “in vogue” in the last year or so. from oven mits, to muffin forms… why the sudden boom?)

I can see how a metal model could be used to create a reverse silicon mold. But I’m not so sure about how you would get the part out of the mold.

  • Isn’t the opening where the handle goes into the brush head a bit small to stretch over the entire brush?

  • Wouldn’t the tiny bristles snap when being pulled from the mold?

Also, there is something that looks like a small “seam” where the bristles attach to the brush head. so perhaps this is a 2-part silicon cast mold. one part holds the bristles, and the 2nd the head. silicon is poured in the top, then when cool, the top of the mould comes off, then grab the brush head and pull the bristles out of the mold.


Can’t tell about the line from the photos, but it sure looks like the bristles are tapered. That alone suggests ejection in the direction of the the bristles’ axes. Don’t forget that their is probably some kind of release agent coating the tool.

If it were up to me… I would have a 4 part mold. The bristles, two halves for the body and the holes for the handle. Inject the plastic, cool enough to remove the handle core. Insert the wire (with a barb on it) handle, then undo the two cavity halves and eject from the tapered bristle section. It might even be injected with the wire handle in place.


I don’t give a rat’s ass how it’s made… … . I just want one. I’m tired of bristles in my barbecue. I was wondering Saturday afternoon if a silicon basting brush was out there. Who is the manufacturer?

BTW, just kidding, I do give a rat’s ass how it’s made.

Perhaps they are mined out of the ground and then graded for size.

But it looks injection molded to me with the ‘base’ of the bristles being the primary parting plane. Is there any indication of where it is ‘gated’?

Lmo: it was a christmas present so i have no idea where it was bought and there is no identifiable marks on it. It seems like everyone is making silicon tzchotchkas for the kitchen these days, so i’m sure you can find one in a dedicated kitchen store. (i certainly don’t think the metal handle would be so great for the BBQ!)

You know, i can’t believe I didn’t think of the “base of the bristles being the parting plane” before. Of course! forhead slap

Not sure what you mean by “gated”, but there definitely seems to be a seam at the base of the bristles.

A bit OT: Isn’t it hard to injection mold brush bristles? they are about 1.2-1.5mm thick at the end, but still I have trouble visualizing how hot silicon gets pressed into a tiny cavities like this. (or are there little air holes at the end of each bristle cavity?)

I’m pretty sure I saw something similar at Crate & Barrel recently…


Considering the excellent thermal insulation ability of silicon the metal handle probably wouldn’t get too hot (unless I left it on the grill itself) … not an unforseeable situation … :neutral_face:

The ‘gate’ is the point at which the material is injected into the mold cavity. It’s usually in an ‘unseen’ spot. But it could be what is/was called a ‘submarine gate’ … this type of gate is located in other than a parting plane, like on the side of a part … when the part is ejected the still molten material is sheared off as the part leaves the mold.

The tips of the bristles would be vented to allow the material to be injected all the way to the tips of the ‘bristles’, and it wouldn’t require much … maybe .0005"

… the ‘sub gate’ in this part may be in one of the two holes that the handle is inserted into.

one more …


Silicone is usually injection molded as a two part liquid that have a chemical hardening process in the mold (kind of like epoxy glue). In it’s liquid state it should not have a hard time making the tips of the bristles. I worked with silicone in the infant products world, but I have seen very tapered silicone parts in the medical world.

This has been quite an interesting topic to read through…

Timf I think hit the nail on the head, I have had some experience with this kind of material before myself.

LSR or Liquid Silicon Rubber is supplied as two different components. Seperatly they are non reactive and have a very long shelf life. However, when the two are mixed prior to injection the compound becomes reactive. On most occasions LSR components have a very rapid cycle time due to cooling quite quickly.

my favorite part of reverse engineering is the actual bandsawing… not that this thing is that complex, but it might answer how the handle is captured. It might be an insert molded handle.

where can i get the liquid silicon rubber for a personal project?


if i’m not wrong here, the only real useful molding technology for silicone is LIM, Liquid Injection Molding.