A bridging panel is one of the components that makes up modular fitted bathroom furniture. In the diagram below the rest of the components have been faded-out to highlight the bridging panels.
In most modular furniture the bridging panel will be made form a wood based particle board covered in a foil or laminate surface. They will be available in various lengths and usually different depths. They are usually fitted in a long run encompassing several units (if fitted) which helps tie the units together both physically and visually, although they sometimes span just one component. So in the following diagram there would be 3 bridging panels:
The first panel would be used for the top of the tall base unit. This has to be separate as base units are usually deeper than wall units. The next bridging panel would run across the top of the wall units, so would not be as deep as first panel described. The third panel is the same depth and width as the second.