Does anyone know whether the cheap soap and candle that you buy, whether they can be melted down to make new ones? I have loads of leftover bits that arn’t any good but the supplies to make the soaps and candles are really expensive/

It is a simple matter to melt and remold candles into new ones. Soap is a little more difficult. I shred the leftover soap bits with a cheese grater, mix with a little hot water and heat gently on the stove until it is fairly runny. They can then be set in a mould to be cut up and re-used. Muffin tins make good soap moulds.

I’ve heard several types of methods, but are unsure of any of them.

Is it true that you can make a stretchable/rubbery mold for odd shaped soap out of caulking? If so, how?

( Odd shaped meaning, not a one sided product like a bar of soap with a rose on it. More like a long stick with a ball on the end. While keeping it a one peice mold, if possible. )

Liquid latex could work for this, the type of latex you use to make moulds for plaster or theatrical masks. You will need a template and coat it with latex and it will be flexible enough.