Buy a variety of goods, pay special attention to their packaging, think about how it talks to adapt to create soap unusual shape and how comfortable will the resulting soap to use.
Then notice that the soap after curing is in no hurry to drop you in the palm of your hand. This is because the plastic is too hard. To remove soap from molds like this, it is necessary to first freeze and then dip in hot water, or to bend each wall of the form and then flip over and press down. Or at least to pick up the edge with a fork or knife blade.