The two types of gels used in capillary electrophoresis are permanently coated gels and dynamically coated gels. 

• Permanently coated gelsare prepared inside the capillary by polymerization of monomers. One example of such a gel is a cross-linked polyacrylamide. This type of gel is usually bonded to the fused-silica wall and cannot be removed without destroying the capillary. 
• Dynamically coated gelsconsist of hydrophilic polymers such as linear polyacrylamide, dextran or cellulose derivatives. These polymers are soluble in aqueous separation buffers, creating a separation medium that serves as a molecular sieve. Unlike permanently coated gels, dynamically coated gels are simpler to prepare because they don't require cross-linking. They can be prepared in a vial and then introduced into a capillary without generating electroosmotic flow, using pressure to fill the capillary walls.