A capsule comprising a core and a shell surrounding and enclosing the core, the shell comprising at least one first polymer having a first water solubility parameter, and at least one second polymer having a water solubility higher than the first water solubility parameter, wherein the second polymer is crosslinked, and/or all of the at least one second polymer is present in an amount that is less than all of the at least one first polymer. Upon exposure to an aqueous medium, the first polymer begins to swell, and water begins to leak into the capsule. Also, the second polymer is attracted to the entering water. As the second polymer absorbs water and swells, the mean free space in the shell decreases and the tortuous pathway for materials crossing the boundary of the wall increases. As a result, leakage rates across the capsule wall decrease.一種包含一核心與一圍繞包圍核心之外殼之膠囊，此外殼包含具有第一水溶性參數的至少一種第一聚合物，與水溶性參數高於第一水溶性參數的至少一種第二聚合物，其中第二聚合物具有交錯鏈結，及/或所有至少一第二聚合物的含量皆少於所有至少一第一聚合物。當暴露於水相媒介內，第一聚合物開始膨脹，且水分開始滲入膠囊。同時，第二聚合物受滲入水分的吸引，當其吸收水分而膨脹，膠囊壁內的平均自由空間減少，且物質穿透膠囊壁阻礙的曲折路徑增加，造成穿透膠囊壁的滲透速率減慢。
