I was wondering the same about releasing the soap, and was thinking that they'd probably have to go into the freezer. But still, the rigid sides would probably make unmolding very difficult.
I have a bunch of these molds in different shapes and sizes. They work great for lotion and shampoo/conditioner bars as well. They're a nice thick quality silicone and have a raised lip at the top that gives a 3D effect and a nice finished look to the bar. They're not fully 3D tho.
You have to make sure you put your soap in the fridge before you stretch and pop them out. https://www.bakedeco.com/detail.asp?id=31644 Silikomart Flexible Silicone Bakeware.
The Bakedeco website has a lot of other silicone molds also and have them at the best price I've found so far (and you can usually find a coupon somewhere! They just had a $10 off that expired yesterday).