What causes condensation in tents?
It is generally warmer inside the tent that outside, because the people sleeping in it give off heat. In addition, there is also an increase in the air humidity or the amount of water vapour – due to breathing, transpiration and possibly rising ground damp from the ground warmed up during the day.
Warmer air can absorb more moisture than colder air. If the temperature in the tent is 15°C and the humidity [%rH] is 100%, then approx. 11 g of water will dissolve in one kg of air (in the form of water vapour). For an ambient temperature of 5°C and 70% rh humidity, only approx. 4 g of water will dissolve. This means that 7g of water vapour is converted into water and therefore has to precipitate. In extreme cases, this will actually take place inside the tent, also because it represents a (cooler) barrier (albeit air-permeable), such as is found with a spider’s web, which captures dew drops. Indoors, the humidity can often reach over 100%, which results in the precipitation of condensation water, say, on the cool bathroom panel after a shower.
The smaller the tent, the greater is the effect – on account of the lower volume of air in the tent. Less air movement (a lack of wind will limit the effect of ventilation holes) also leads to a larger amount of water precipitated. For this reason, it is recommended to leave additional parts of the entrances to the tent open. These can be guyed to prevent any rain getting in.
This effect is intensified with silicone-coated tents since silicone – unlike polyurethane (PU) cotton – is not hydrophilic (having an affinity for water). It is unable to partly absorb any condensation water occurring. The benefits of these textiles lie in their higher degree of UV resistance and tensile strength as well as a significantly lighter weight.