A balance is established between the water content of the honey and the surrounding air humidity. The balancing moisture content of honey at a relative humidity of 55% is about 17.5%. At a relative humidity of 80%, honey has a water content of over 30% (source: The hygroscopic properties of different dilutions of Honey, Doull & Mew 1977).
The wax capping of the honey cells slows down the speed of these water transports, but does not prevent diffusion.
The amount of water vapour diffusion resistance of the honey cell caps has to be finally determined. Own observations / tests give a contrary result: On the one hand I was able to determine a water vapour diffusion resistance factor µ of 330, on the other hand weight measurements of honeycombs, which were exposed to changing air humidity, indicate a µ-value larger than 10000.
In the second case, the honeycomb cap could no longer be classified as open to diffusion, but as diffusion-inhibiting. Water would still diffuse through the caps, but the amount of water would be negligible compared to the other water transports in the bee habitation.