The underwater housing fits the camera like a glove. This makes it hard to fit a sachet of silica gel in with the camera.

The sachet of silica gel is necessary because of the heat the battery and the internal flash produce.

This heat cannot find a way out of the polycarbonate housing and will eventually condensate. Moist and condense is a killer for digital cameras so you need this sachet with silica gel to absorb the damp.