What is the difference between stacking gel and resolving gel in SDS-PAGE?

Stacking gel and resolving gel are two types of polyacrylamide gels used to get better separation of proteins in each sample. These two gels differ in pH, polyacrylamide content, pore size as well as ultimate purpose.

• Stacking gel has a lower pH (6.8) than the resolving gel (8.8).
• The polyacrylamide content in stacking gel (usually around 4%) is lower than that in resolving gel (around 10%), which leads to smaller pore sizes in the stacking gel.
• The purpose of stacking gel is to line up all the protein samples loaded on the gel, so that they can enter the resolving gel at the same time. The resolving gel is to separate the proteins based on their molecular weight.