Best process for mfg a pp handle?


I am designing a commercial kitchen utensil that will be used several hundred times a day. As a result I’ve designed an ergonomic polypropylene handle that has a substantial amount of material (so it cradles in the hand).


  • One mfgr is suggesting a single injection mold.

  • Another mfgr is suggesting using three molds. The first part is a two piece handle that snaps together then gets an overmold with the final handle shape and finish.

Does anyone have experience with these different processes? Are there any pro/cons that I need to consider?

Thanks for your input!

-how substantial is “substantial”? Are they going to core out a bunch of material from one pull direction if mold it in one shot?
-1 set of of tooling is always be cheaper than 3 sets of tooling.
-If there’s an over mold in the design intent, you need two tools anyways. How is the first molder going to achieve that?


It does sound like the first option will have HUGE cycle times and prone to sink marks.

The second option will have a higher capital cost, but likely a lower part cost.

So again, it depends on the final design and volumes.

Thanks for the replies. Comments below.

Substantial: Well, the best description is if you stick an small size computer mouse on the end of a stainless steel ladle.

“Are they going to core out a bunch of material from one pull direction if mold it in one shot?”
I guess I don’t know what you mean. Can you clarify?

Yes, the tooling more expensive, but the part price offsets it considerably. Not a total wash, but enough to consider both mfgrs.

There is no overmold in the design. It’s all pp with a texture . Simple enough.

Ya, I was concerned about sink marks and overall QC. What do you mean by cycle times?

If the part is large, you need to wait longer for it to cool before ejecting it from the mold which leads to less parts made per minute hence longer cycle times.

one issue that nobody mentioned is manual labor. the multi-tool option would most likely require additional labor (more cost) and with labor costs increasing in china (i’m assuming that is where you are thinking of mfging) that is an issue as well.

Cycle time = the amount of time it takes for the mold to go through 1 cycle of molding = opening & closing time + injection time + cooling time + ejection time

Basically, you are renting time on someone’s injection molding machine. The cost of the run is the set-up time + running time + tear down. Running time is the only variable. The faster the cycle time, the lower the running time, the cost goes down. If you are running very high volumes, a lower cycle time will increase capacity so you may only need a 4-up tool (less cost) instead of an 8-up tool.

That may have been part of Brett’s point. The large single shot could be reduced if you have it hollow but one side of the part needs to be “missing”. Think of your small mouse. From the top it looks solid. If you flip it over, it would be “hollow” but with honeycomb walls for strength.

For the multi-shot, that can be completely automated with spin-stack technology, no labor, but increases tool cost. Juno does that type of work. JunoPacific - Home

Are the two snap together parts creating a hollow “core” and the “over-mold” is PP molded over the inner core. Basically an over-mold part but using the same/similar material?

If this is the case and your design isn’t terribly asymmetrical, this “core” can be made from one part. It would be 2 of the same part that can snap to itself. This is often done with a female snap on one half and a male on the other so that when it is turned face to face the male/female and female/male sides align. The outer mold could have variable walls and create the form of your design. Now you have two molds, not three.

I’d think that the 3rd option would be 2 halves that snap together with care that the parting line not running across the users hands. I’d assume this would be around the sides. This is usually OK with silicone.

I think we’re looking at this wrong. A simple handle on a cooking tool for use in a commercial kitchen really wants zero part lines on it. It should be as seamless as possible, 1 piece.

I don’t want any part lines on the final because it’s used several hundred if not thousands of times a day -a comfort issue.

Another reason I don’t want part lines or hollow pieces is so it won’t harbor contaminants that could introduce a health/safety risk to the customer.

Polypropylene was chosen for durability and color fastness.

Thanks again for all the input. Keep it coming.
This is one of the first contract projects i’ll manage the design AND mfg on, and definitely my first utensil.

Right, I totally agree with you. I was just trying to understand what the second vendor was proposing (overmold, yet you say your design has no overmold ?). No matter what you will have some flashing, but it can be minimized. You don’t feel the flashing on a silicone handle, so it’s only an aesthetic issue then.

I don’t know about molding PP parts that thick though. As mentioned, I’d worry about cycle time contributing to cost.

If this is a confidential project I would be happy to sign a NDA and then you could share an image with me. We can go from there and I can let you know the pros and cons’ along with various manufacturing options. And Design options that will allow you to keep design intent and meet manufacturing and costing. I have over 13 years of experience designing for manufacturing with 6 of that do kitchen products.

Also on a side note, I can’t say for sure without seeing the design or knowing the product but your ID requirements may be a little extreme. You can contact me via and we can go from there. I can also explain to you quickly what the over mold option the manufacturing is talking about along with its pro’s and cons.

Is is feasible to do a polypropylene “slug” injection around the stainless steel handle initially, and then do final handle shape as a pp overmold?

This would only require 2 tools, and no need to snap any parts together before overmolding.

I may take you up on your offer. I’m pretty busy right now, but maybe I can squeeze some time in the next day or so.

Again, thanks for all the great input!

There are ways to mold thick parts with hollow interiors to keep the plastic mass down maintain a reasonable cycle time. Gas assist molding or water injection parts are made like this:

You should be able to find example in the marketplace of hollow molded one piece handles.

If you are set on Polypropylene, check out Tegris. It’s a pp sheet made by weaving pp sheet. Each of these sheets is then laminated into a composite.

It’s like a poor mans carbon fiber, (~1/2 as stiff and 1/10 the cost… check those numbers, but they are close), but it’s also food safe (pp, after all) and recyclable.

Only downside is that it’s sheet, so to get a gas-assist-esque shape, you would have to bond to separate halves, not as clean.