The soft capsule shell is thicker than the hard capsule shell, and has greater elasticity and plasticity. The elasticity of soft capsules depends on the weight ratio of dry gelatin, dry plasticizer and water in the capsule shell (the plasticizer is glycerin, sorbitol or a mixture of the two). The dry weight of gelatin and plasticizer determines the hardness of the rubber shell. Usually the more suitable weight ratio is dry plasticizer: dry gelatin=0.4～0.6:1.0, and the ratio of water to dry gelatin is 1:1. When the weight ratio between some plasticizers and gelatin is 0.3:1.0, the rubber shell becomes hard, and when the weight ratio is 1.8:1, the rubber shell becomes soft. The ratio of various materials in the plastic shell prescription is determined according to the nature and requirements of the drug. Therefore, when choosing the hardness of the soft capsule material, the nature of the filled drug and the interaction between the capsule material and the drug should be considered. The nature of the drug should also be considered when choosing a plasticizer.