The physics behind the condensation in tents?

Question

When you compare single wall tent to double wall tent usually you will hear short summary "double wall tent prevents condensation from building up".

So in most fair comparison it should work like this -- I have imaginary single wall tent (i.e. tent with only one layer, the rainfly) and using it will cause condensation to build up. OK.

So now let's add to this tent inner tent (mesh layer) and this prevents condensation.

Hmm... I don't see it. I mean, condensation occurs when the warm air is cooled down to the point it no longer can hold steam. I guess the mesh barrier can slow down the process (i.e. you would have warm space inside, middle space between layers, and the cold air outside), the warm air from inside not so soon reaches the outer layer. But eventually it will reach it.

Second guess would be that inner mesh gets a little wet, and by this it helps the air to hold the rest of the amount of steam. But this effect I would say is a condensation anyway, just not visible because of the nature of the mesh.

So is there any other effect that contributes to the notion "inner tent prevents condensation"?

Answer 1

They don't prevent condensation. They just reduce the chances of condensation getting onto your kit down to practically nothing, if you do it right.

The condensation stays on the inside of the outer layer. Your kit is on the inside of the inner layer. The condensation doesn't cross the gap between the inner and outer layer. It runs down the inside of the outer layer. And then it can't pond inside the inner layer.