Olympus Silica gel will help prevent condensation from forming inside a housing. Condensation will form in a housing when you take it from warm air to cooler water. Internal camera flashes being fired inside the housing will compound this problem.
Since the silica needs some time to act, give it about 10-15 minutes after closing the housing before entering the water.
Silica Gel Desiccant for Olympus Underwater Housings
Silica Gel Desiccant