A protective padding system is provided in which a padding member has one or more cavities formed therein. The padding member preferentially flexes at the cavities. An insert is adapted to selectively engage and fit into the cavity. When engaged, the insert reinforces the padding member at the cavity, and thus reduces or eliminates the flexibility of the padding member at that location. By selectively engaging or disengaging an insert, a user may customize the flexibility characteristics of the padding member in a reversible manner.