What is the principle of the inner mucous membrane of the silicone doll?

In daily life, when their wives are pregnant or have frigidity, men’s physiological needs are not met, and they will think about buying a silicone doll. So how far has the current silicone doll development been? In addition, what is the principle of the inner mucous membrane of the silicone doll? Speaking of silicone dolls,…