Article by NEMO Minimizing and Preventing Condensation in Your NEMO Tent Condensation inside your tent can be the scrooge of any camping trip. Learning to minimize and even prevent condensation can greatly improve your camping experience — keeping you warm and dry for your adventures! Defining Condensation Air holds moisture in the form of water vapor. There is a limit to how much moisture air can hold which is partially dependent upon the air temperature (warm air can hold much more moisture than cold air). When the water vapor level in the air reaches this limit, that air is defined as saturated. The amount of water vapor in the air is measured by humidity. The term relative humidity (RH) describes the amount of water vapor in the air relative to the total amount of water vapor air can hold at saturation (saturated air is equivalent to 100% RH). Since cold air holds less moisture than warm air, a minimum air temperature exists for a given amount of air before the water vapor changes to liquid (condensation). This temperature is called the dew point. Condensation occurs when 1) warm, moist air meets a cooler surface and is cooled below the dew point or 2) air is already at 100% RH while moisture continues to form. Environmental Conditions Favoring Condensation As air temperature cools during the night, relative humidity tends to increase because the amount of water vapor in the air stays the same, but the total amount of water vapor that can be held by the air decreases. In cases like these, condensation will occur. The worst cases of condensation occur during cool temperatures, high humidity, and very little wind. On cool, still nights, there is very little air circulation between the warm air inside and the cool air outside your tent. Without a shell fabric that transports water vapor out, condensation can quickly accumulate on the interior surfaces of the tent. Certain environmental conditions such as subzero climate and heavy rainfall can increase condensation. In high altitude, the decrease in atmospheric pressure reduces the resistance to water vapor, also increasing condensation. Sources of condensation Humidity from your breath (1–2 pints per night). Evaporation of sweat and moisture from clothing Humidity from the ground High humidity in the air because of close proximity to lakes or rivers Steam from cooking too close to the tent Humidity from increased elevation Cold ground under sleeping pads Which Tents Are Affected the Most by Condensation Single-wall shelters like the Spike™, Chogori™, Wagontop™, and Tenshi™ will require extra care in set-up to mitigate condensation. Because these are single-wall shelters, crosswinds aren’t able to circulate into your tent to air it out like a double wall shelter. Our single-wall shelters feature vents in the doors and top of the tent — we highly recommend using these when the weather allows it. Tent Setup Tips Set up your tent correctly with proper tension. A taut tent body that is staked and guyed out well will prevent water from pooling under the tent and let the fabric breathe. Pitch your tent away from bodies of water. A tent should be staked out at all four corners, with the addition of the stake-out points on the rainfly. Make sure there are no wrinkles in the fabric so that the DWR on the fabrics can bead correctly and keep you dry! Set up your tent on high ground where it is more likely to take advantage of some wind. As a rule of thumb, if the wind is roaring outside, pitch the shortest end of the tent into the wind to take advantage of aerodynamics. If conditions are calmer, face the largest vents or mesh areas into the wind for increased cross ventilation. Use windows, doors, and vents to achieve optimum airflow. Create a passive “high-low” airflow system where cool air enters from ground-level vents and hot air is expelled through roof-level openings. Many NEMO tents offer a vent strut on the rain fly zipper. Use this strut to help prevent condensation. Avoid keeping your wet gear inside the tent to dry. If there is condensation on your tent walls when you wake up in the morning, wipe down the interior or shake off the moisture before packing up the tent. Resist the urge to throw your gear in the corner until your next trip — hang up the tent in a dry, well-ventilated area to avoid mold and mildew on your next camp outing. If you do notice moisture on the inside of the shelter, feel free to wipe it away with a towel or other absorbent material. A common myth is that touching a wall or roof during a rainstorm will make liquid travel through the fabric — this is completely false and keeping the inside of the fabric dry actually allows vapor to escape more efficiently! Have any questions? Reach out to our Customer Service team here or at 800-997-9301.