[Terminology] Reversible gel and irreversible gel
Reversible gel, also known as elastic gel. Reversible gel is freely interconversion with sol state and gel state.
Many substances can form the reversible gel, such as: gelatin, agar etc.
Irreversible gel, also known as non-elastic gel. Irreversible gel is not freely interconversion with sol state and gel state.
Silica gel is widely used is the irreversible gel.