Closed-cell self-expanding foam (spray foam) is an amazing material that sees common use in construction. But one application that we hadn’t heard of before was using it to fill the internal voids of 3D printed objects. As argued by [Alex] in a half-baked-research YouTube video, this foam could be very helpful with making sure that printed boats keep floating and water stays out of sensitive electronic bits.
It’s pretty common knowledge by now that 3D printed objects from FDM printers aren’t really watertight. Due to the way that these printers work, there’s plenty of opportunity for small gaps and voids between layers to permit moisture to seep through. This is where the use of this self-expanding foam comes into play, as it’s guaranteed to be watertight. In addition, [Alex] also tests how this affects the strength of the print and using its insulating properties.
The test prints are designed with the requisite port through which the spray foam is injected as well as pressure relief holes. After a 24 hour curing period the excess foam is trimmed. Early testing showed that in order for the foam to cure well inside the part, it needed to be first flushed with water to provide the moisture necessary for the chemical reaction. It’s also essential to have sufficient pressure relief holes, especially for the larger parts, as the expanding foam can cause structural failure.
As for the results, in terms of waterproofing there was some water absorption, likely in the PETG part. But after 28 hours of submerging none of the sample cubes filled up with water. The samples did not get any stronger tensile-wise, but the compression test showed a 25 – 70% increase in resistance to buckling, which is quite significant.
Finally, after tossing some ice cubes into a plain FDM printed box and one filled with foam, it took less than six hours for the ice to melt, compared to the spray foam insulated box which took just under eight hours.
This seems to suggest that adding some of this self-expanding foam to your 3D printed part makes a lot of sense if you want to keep water out, add more compressive strength, or would like to add thermal insulation beyond what FDM infill patterns can provide.
It’s great for automotive body and frame repair too! (just kidding!!!!)
Hey, don’t knock it. I made it through a couple of years with a Datsun held together by polyurethane foam with old licence plates brazed on to add structural support and fill the bigger holes. Some Bondo and rattle-can top coat and it doesn’t even look too awful.
You can infer from the name “Datsun” that it predated all this airbags and seatbelts and crumple zone stuff, so it was perfectly safe to do body mods like this: they didn’t reduce the safety of the car at all!
No to frame, yes to body repair! Placing a couple trash bags between inner and outer shell of an old van and filling with foam kept mice out (don’t know why), and air leaks for a few years… not kidding
I used this ages ago to make little boats that floated around and measured turbidity in silt settling ponds. They all eventually waterlogged and sank (to some degree) but some lasted quite a while. Sections of PVC down pipe, capped at both ends and braced to make little Catamarans were the answer.