This is a large box-style soap mold used for pouring a large amount of soap, letting it set, then cutting the large block into smaller bars. The SketchUp file is included under Thing Files.
Using cellophane to wrap each part, then assembling with M6 x 100mm bolts (at least 4 bolts per box) ensures a pretty solid fit with little leakage. Keep the box on a plastic bag or other easily washable or disposable cover anyway just to make sure.
It is easy to make these from wood but we live in the center of the city, finding wood for projects is difficult, and we really don't have an appropriate place to cut/drill. 3D printing was the perfect process and allowed us to make the molds exactly how we wanted.
If you're new to soap making like we were when we first tried this project, check out: https://www.soapqueen.com/
They have excellent videos on YouTube & an ingredient calculator to help you with your recipes.