This might be too much mold info, but it's easier to copy/paste from my blog.
PVC Pipe – Great for making round soap. Molds don’t need to be lined but can be prepared with mineral oil to help soap release easier. After pouring in soap, cover with plastic wrap and a dish towel to insulate the top of mold. Leave soap in mold for 24-48 hours, pop in freezer for an hour and push soap out one end. Slice to desired thickness. I typically get a full gel using PVC pipe. These are the molds that I use in all of my Cold Process Soap classes that I teach. They’re inexpensive and can be used over and over again.
Yogurt cups, Cream Cheese containers and other plastic food containers – Great for small batches or “overflow”. I keep a handful of these containers around for left over soap after I’ve poured my wooden loaf mold. They do not need to be lined.
Shoe boxes and other cardboard boxes – These molds need to be lined. They must be insulated well if you want a full gel. Use towels, blankets and even a warm heating pad to help force gel.
Plastic storage boxes and Tupper Ware containers – If containers are thicker and not easily flexible, you will need to line in order to remove your soap easier. If the container is more flexible, then you may not need to line. They must be insulated well if you want a full gel. Use towels, blankets and even a warm heating pad to help force gel.
Silicone Baking Ware – Great for soaping! These types of molds do not require lining and soap is easily removed because of the flexibility. They must be insulated well if you want a full gel. Use towels, blankets and even a warm heating pad to help force gel. Since silicone can withstand high heat, you can even put your mold in a warm oven to help force gel.
Pringles Cans – Can be used lined or not. If not lined, you can simply peel the container away from the soap and throw away. If you line with freezer paper, you can sometimes get more than one use out of the container. They must be insulated well if you want a full gel or can be put into the fridge or freezer to prevent gel.
Orange Juice Containers – Square cardboard orange juice containers make great molds and produce large square bars of soap. You do not need to line them since they have the waxy coating to begin with. Once your soap hardens you can peel away the container. They must be insulated well if you want a full gel or can be put into the fridge or freezer to prevent gel.
Other molds you can use include wooden drawers, cigar boxes, shipping tubes…the list goes on and on.
Hope that helps!
Amanda
