DIY
Positive mold of a polypropylene cavity
I’d like to make a positive mold of the pictured cavity on a Pelican case, in order to design an attachment, but I’m concerned about the material sticking to the inside. Is there a preferred material for this, or some way to ensure it comes out smoothly? I tried googling it but all the results were about molding polypropylene itself. Thanks!
Discussion
A pourable silicone is not likely to stick aggressively if you apply a little mold release in the cavity. The harder the product you use, the harder it will likely be to get out.
No matter what you do you should be prepared to drill a small hole in the bottom of the cavity so you can blow air into it to pop out the positive.
Cast a drinking straw or tube into your mold material to include an injection point for the air to pop it free.
And a popcicle stick to pull on while you're at it.
Maybe you could line it with Saran wrap or some other non-stick paper maybe?
Or maybe coat with a release agent of some kind
Yeah that’s probably the way. Plastic wrap would work great
Getting plastic wrap up into that hole might be a challenge but I agree it's the best way. Look up how instapak foam packing material works. perhaps you can trim+reseal a ziploc bag or similar?