If you are using the camera in an environment where the inside of the housing lens is fogging up during use, we do have the Anti-Fog Inserts designed specifically for the HD HERO camera. It will help to prevent your camera's housing from fogging, even in cold temperatures/humid environments. The kit includes 3 sets of anti-fog inserts, and retails at $14.99. Each set lasts 4-5 uses and can be dried in an oven (3 minutes) and used again.
Please note, if you are using the camera in conditions where waterproofing is not needed or where high wind noise is not an issue, then you should use the open back door for the housing. Using the open back door for the housing will ensure that the temperature inside and outside of the housing is equalized, thus preventing fogging.
The one button mode feature added to the HD HERO Original camera through our camera software update is also a great feature to help prevent fogging. This feature will have the camera automatically fully power off when stopping recording. When the camera is powered off, it will not be generating heat which can cause fogging.