Making a Skinny and Tall Soap Mold

A homemade, rectangular cardboard box—repurposed as a tall soap mold—has uneven edges and clear tape along the sides. One flap is partially open, extending outward. Carpet and wooden furniture are visible in the background.

A rectangular cardboard box resembling a skinny soap mold sits on a dark surface, one side partially open with an extended flap. Handwritten measurements and markings are visible inside the box.

For my last published soap project, the peacock feather soap, I needed a tall and skinny mold. I usually prefer the short and fat molds (I guess that would be their name?) so I did not want to spend money on buying a mold I would only use a few times.

I had made one in the past, but too large, so this time I tried to make a smaller one. It is a fairly simple process. Here is what you will need if you want to try it:

A good pair of scissors (the kind that can cut through cardboard with no problem)
A long ruler, at least 18′ long
Two cardboard boxes. One for the mold, and one to protect your table
A pencil and ballpoint pen
A box cutter with a sharp blade

The Process

First decide what your mold size will be. I wanted mine to be 12″ long and 2.5″ wide, and 3.5″ tall. Because I knew I would lose some measurements to the liner and the walls of the cardboard, I measured my lines to be 1/8″ longer, wider and taller.

In cm, these measurements would be 31 cm long, 6.35 cm wide and 9 cm tall

2. Secondly, open the box you will be using (a fairly large one) and use one of the creases to be one for your mold. In this case, I am using the left crease as the crease between the base and wall of my mold. So I marked 2.5″ marks from that end (7 cm). I made two marks, one on top and one on the bottom.

3. I aligned my ruler to the top edge, and I made sure it touched both marks, so I could make the first line with the pen:

4. From that line, I could start making my other crease and cut lines, following the same process. What I had marked now was the bottom, so I needed to mark the walls on each side, which would be 3″ (9 cm) from the crease, and from the line I just drew.

5. I use the creased on the top as well, as the side crease, ad measured 12″ (31 cm) to the opposite end. After that I cut out what I did not need, and kept just the outside lines I had drawn:

6. I cut flaps on each end, so that it would not be super thick with three layers of cardboard intercepting, and instead, the two tabs would meet, like this:

7. With the ballpoint pen, and went over the wall line again, to create a crease mark and folded the wall up:

8. I repeated the process with all the other line marks. and I put clear tape around the edges, and all over, so that dthe soap would not get it wet.

I taped the ends close and then made a plastic liner, but a parchment paper liner would also work.

Making the Liner

I have made a previous blog about making a plastic liner before. You can read that here. I used an expanded legal size folder, (like this one) for it, and here are the steps:

From the edge of the folder, measure the first wall, so make marks at 3.5″ or 9 cm, make a couple or marks like in here:
Draw a horizontal line that goes through the marks, and then from that line, measure 2.54″ or 6.3 cm
For the length of the mold, measure 1.5″ or 3.6 cm, and from there, measure 12″ or 30.5 cm Repeat the measurements on the other side until you have something like this:
Cut the excess plastic and start coring and folding at the lines:
Here I am using the handle of the scissors to crease the fold
When properly creased, you will see the white inner plastic showing a bit.
You could tape the ends when you are ready to use, I recommend using sodium lactate as plastic is not porous like paper, so it does take longer to be able to come out of the mold.