Round Soap Molds

Iron City Trading sells a lot of soap, which means we get to make a lot of soap. When I say we, it’s mostly my wife. She researches the oil blends, calculates the recipe, and makes the product. We wanted to make some round soaps, so I made molds using 3″ PVC drain pipe. It turns out that a batch of soap nicely fills a tall (20″) and a short (12″) mold, so I made some of each height.

img_0120The trick with these PVC molds is to get them to be stable while being filled, and while the soap hardens. They need a good base for stability, but it needs to be removable to allow the hardened soap cylinder to be pressed out. We use a tubular plastic liner so that the soap will more easily release from the mold.

When looking for a base for the mold, my first thought was to use a standard PVC pipe cap, but all the ones I found were rounded on the end, and unsuitable to use as a base. I found a PVC toilet flange (the part that sits on the drain pipe and is used to attach the toilet to the floor) to be the answer. The flange I selected was made of PVC and metal, and had a knockout plug in place, sealing off the end of the pipe, so that was perfect. The metal ring was pressed into place and unforunately, was very sharp around the edges, so I decided it would be best to remove it.




  • 3″ diameter PVC pipe (12″, 20″, or the length you need)
  • 3″ toilet flange(s) with knockout plug in place (one per mold)


  • Hacksaw (if you need to cut the pipe to length or to cut the metal flange)
  • Electric drill and 1/4″ bit
  • Sandpaper
  • Gloves and safety glasses

Steps to Make the Molds
(1) Gather the materials. Cut the tube to the correct length using a Pipe Cutter or hacksaw. You may need to sand the edges of the pipe to get them smooth.








(2) Prepare the flange. To remove the metal ring, I used hand tools to cut the sharp metal ring and then used pliers to remove it. Use caution because the metal edges of the ring are sharp. Once the ring is removed, the remaining part of the flange is all PVC and is safe to handle. Even with the metal ring removed, the flange provides plenty of stability for the mold. In the photos below, I prepared two flanges.








Tip: Use a tubular plastic liner to make the soap release rom the mold more easily. The liner can be folded over at the top and secured with a rubber band. These liners are available from online soap supply companies.

(3) One problem with using a liner is that air needs to escape from the space between the liner and the tube as the mold is filled, otherwise, the air space will cause voids in the soap. To alleviate this problem, I drilled a vent hole through the flange and the tube, near the bottom. To do this, assemble the mold and drill a 1/4″ hole near the bottom of the flange.



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