Roto Molding

Anyone have any info. or experience in roto molding?

  • Manufacturers to speak to
    *Is tooling exspensive?
    *Whether its a good way to go for low- mid volume production. Any kind of info would help to start.

Is there anything in particular. What stage are you at. I’ve designed and engineered for the process.

Seating. In design stage now. Just want to be thinking about manufacturing in the back of my mind while designing.

Well, you may not really need to worry about draft so much, as the tool with be able to “disassemble.” Factor about .5" nominal for all radii. Wall thickness will vary, so keep your aesthetic surfaces relatively simple. Plus, the surface finish will not be A-class, so high polish may not come out well. Panel cut lines will suck as the gaps and radii will really stick out. Lastly, find a good shop you can work with on pricing and who can view CAD models easily. Have lots of meetings. Chances are your proto may also be your first article production. It’s a crude process, so make sure your aesthetic plays it up well. Good luck

Its been a while, but a rotomolding vendor introduced us to a process where a ‘sandwich’ was made. The surface material (polypro I believe) was done first, to a thickness of around .25", and then a polypro ‘foam’ was somehow injected inside of the outer surface. This made for an ice cream sandwich-like part of amazing stiffness, and could be applicable to your seating project.

Masood, I like your Coroflot portfolio, esp how you did the PDF viewing embedded in the images.

Thanks for the pointers. Recommend any manufactures near bay area?

SF: Thanks for p’folio shout-out. By any chance would you happen to have any pics of the roto-mold part you’re talking about?

GeraldS: My client used a vendor out in the midwest for their respective roto-molding. “You gotta go where the love is.” At least for rotomolding. I’ll try and locate the source. Did you check out Thomas Register?

This first image is of the wooden buck that was used to cast the rotomold tool. It will make a nice coffee table someday.

This is one of the final parts. I don’t have a cutaway showing the foamed PP inside, but rest-assured, this part will be around until the Earth is hit by an errant comet 10,000 years from now, and may even survive that.

Hi GeraldS

I would like to interject because I don’t agree with some of the points of masood1224. A lot of the information you’ll receive is based upon the typical lecture on Rotational Moulding that most Industrial Design students will experience at some point during their course.

I develop rotationally moulded products on a daily basis and I have come across a lot of people who see the process as being ‘crude’, however, this isn’t the case and you can achieve very high quality finishes given the correct design, tooling, polymer and processing conditions.

My advice would be to concentrate on the first 2 requirements; design and tooling, because the others are variables that can be determined later.

Tooling options include sheet steel, cast aluminium and machined aluminium. The pattern shown by slippyfish will have been used to create cast tooling. Tooling costs can vary considerably depending on process, size and complexity of moulding. Machined aluminium tooling is the most expensive route but will also achieve the best finish.

One point to bear in mind regarding complexity of shape is that, although you can split the tool into as many pieces as you like, the product has to be demoulded and the parting lines have to be deflashed - this adds cost at the tooling production and product production stages. Also, parting lines will always be visible to an extent on the finished product. There is a massive amount of information on the web but I’d take as much advice as possible from companies specialising in rotational moulding to find out what is actually possible.

For advice on some basic design considerations, we publish some downloadable guides on our website:

Hope this helps.

Jspen - Thank you kindly for chiming in with great information on the roto process. Having passed my ID materials and process courses, and also having 8+ years in the product development field, by no means should the advice that I give pose to be end all solution/strategy to the rotational molding process. I have also completed a few projects dealing with many components that comprise of a rotational molded panel assembly. However, in light of the ‘crude’ nature, I was discussing in terms of aesthetics. I’m sure there is a thousand different ways to achieve the high quality surface finish on roto parts. However, you yourself stated there may be considerable cost in the post processing that needs to be accomplished to get the high quality finish. In my humble opinion, my job as the designer is not add cost to end part to reach a high quality finish, my job is take the standard manufacturing process and through the proper form and context, achieve a design that allows the audience/user to see past the nature of the finished design without the hangups of parting lines and flashing. In my design, the flashings and parting line add further compositional elements to the work.

I believe Nottingham Spirk penned the best story utilizing rotational molding:

Lastly, if at all possible, could you also provide a few pics detailing some of ideas your speaking of?.


:exclamation: Standing ovation.

An option for low-volume (less than 100 units) would be fiberglass or carbon-fiber molds. The surface quality can be increased by hitting it with a flame gun. Also, by selectively insulating certain areas of the outside mold surface you can control wall thickness.

Hi Geralds, I’ve got a fair amount of experience in rotomolding as well. Contact me directly if you need some advice specific to your application.


I did a tour of Dutchland Plastics (rotational molder in Oostburg, WI) a while back which was very helpful in learning about the rotational molding process. Daven Claerbout is the owner - I’m sure he’d be happy to go over your product and give you suggestions. Cultivating relationships with manufacturers early in the design process is helpful to everyone involved, and they are usually happy to educate you for free if they have a reasonable chance of manufacturing the end product. Kudos to you for taking the initiative to design with the end in mind, instead of pumping out vapid, shiny unrealizable renderings!

Well said.


warrenginn - thanks ill i think i will contact you when i get closer to manufacture.

imadesigner - thanks aswell for your comments. Its always nice to hear comments like yours, when at my work i hear comments like i take too long on projects, it really makes you feel like to i doubt yourself when i hear that, when all im trying to do is to solve the problem from the start. do you have contact info?
Phone: 920-564-3633


If you are still searching for a rotomolder who will help with process feasibility, rotomolding tooling and part quotation. Roto Dynamics Inc. in Anaheim, CA will be able to assist you.

Rotational Molding resources:

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