On The Benefits Of Filling 3D Prints With Spray Foam

November 29, 2025 by Maya Posch 41 Comments

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.

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Tis The Season For Terror With DIY Krampus

November 30, 2017 by Tom Nardi 19 Comments

The holiday season is full of many sounds; walking through your neighborhood on a winter night you may hear time-honored songs, the tinkling of glasses, and the laughter of good company. But if the chilly wind also brings to your ear the panicked sounds of screaming children, you may have wandered a bit to close to [Tyler Garner]’s house.

Rather than old Saint Nick or a couple of reindeer, [Tyler] decided to top the roof of his home with a disturbingly well done rendition of everyone’s favorite��Austro-Bavarian goat-demon, Krampus. While he did finish the build off with a store-bought Krampus mask, every other component was made with about a 60/40 ratio of hardware to craft store scores. While your holiday decorations this year may not include any spawns of hell, the general construction techniques and resourcefulness [Tyler] shows in this build may come in handy when Halloween rolls around again.

The “skeleton” of Krampus is made up of PVC pipes and fittings mounted on an MDF base. Not only do the PVC fittings make it easy to recreate the rough anatomy of a humanoid figure, but if you don’t glue them all together, you can take it apart later for storage. We might have gone with something a little heartier than MDF for the base, but at least [Tyler] added a few pieces of galvanized pipe at the bottom to give it a little weight down low.

Things start to get interesting when [Tyler] adds sections of drainage pipe to his PVC skeleton to give it a more girth, as he was finding the bare PVC didn’t have a realistic presence when the robes were thrown over them. [Tyler] also uses expanding spray foam to soften up areas such as the hunched back, which may look messy but has the dual advantages of being cheap and fast.

The figure’s robes are made up of a patchwork of burlap, waterproofed with a spray on liner intended for pickup truck beds. With the application of red and black spray paint and the customary white fringe, it really nails the look.

A particularly nice detail is the hoof peeking out from beneath the robes, which [Tyler] made out of painted air-dry clay. It’s an awesome detail, though almost impossible to see once Krampus is mounted on the roof. Maybe it’s just us, but we think putting so much effort into a nearly hidden feature of a project is the true mark of a master craftsman; this is a secret little hoof that [Bob Ross] himself would be proud of.

While we can’t say we’ve played host to holiday scamps like Krampus or Belsnickle before, Hackaday has certainly seen its fair share of festive hacks over the years.