I'm sorry but heat does not generate fogging. The housing is waterproof so no water gets in or out, it's purely the water contained within the housing, if the temperature of any part falls below the dewpoint of the air trapped in the housing it will condense on the cold part. What can happen to give this impression is if there is a drop of water which has managed to get inside, which could then vapourise in the heat, this could happen if you open the housing, you often see water drops on the o-ring when the housing is opened and if they get inside then you have a problem. The key is to not trap any water in the housing or very humid air.
Polyurethane foam has very good insulating properties, due to being foamed, thermoplastic polyurethane though has very similar conductivity to polycarbonate as used in ikelite housings, I have not seen an aquatech housing in the flesh, however in photos don't look like they are made of any type of foam. For the housing to feel warm on the outside it would need to be a reasonable conductor of heat. I suspect what is happening is the the Nikon just generates more heat. Is the camera left on when out of the water? How hot does it get?
Heat actually reduces humidity however the residual one you have moves towards the material that conducts more in this case glass of the port. In that area the temperature is lower as exposed to water and this is how condensation forms.
Any object will have residual humidity trapped inside when the battery and the sensor heat up the particles start moving and end up fogging up.
If the housing is made of metal the condensation happens on the metal because it conducts heat more if plastic it tends to go on the glass.
A camera in a plastic housing will always be hotter after a dive than if it was in a metal case
Hence the suggestion of the silica packets. A camera does not generate heat being left simply on. Typically the parts that get hot are the battery, the sensor, the lcd screen. Even the flash doesn’t really get hot in comparison.
Either way the plastic housing will trap the heat
The RX100 in ikelite housing has a lot of volume around whilst the aquatech housing are snug so there is less gas to dissipate heat into
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