A rain fly is the waterproof outer layer of a double-wall tent. It sits over the tent body, which is usually made of breathable fabric and mesh, and it keeps out rain, wind and dew. Some campers use the same name for a separate tarp pitched overhead.
Why tents use two layers
You breathe out moisture during the night. If that moisture meets a single waterproof wall, it condenses and drips back on you. A double-wall design lets moisture pass through the inner tent and away through the gap beneath the fly, which keeps the sleeping area drier.
Main types of rain fly
- Full-coverage flies reach close to the ground and give the best protection from wind-driven rain.
- Partial flies cover the top of the tent, improving airflow on warm nights, but they offer less protection in storms.
- Flies with vestibules create a covered area outside the door for boots and packs.
What to look for
- Material: polyester sags less when wet, while silicone-coated nylon is often lighter.
- Waterproof rating: shown as hydrostatic head in millimeters. A higher number means more resistance to water pressure, and around 1,500 mm or more is a common target for three-season use.
- Sealed seams: water can get in through stitching, so check whether seams are taped or need sealing.
- Vents: adjustable vents reduce condensation.
How to pitch it for a dry night
- Pitch the tent on a slightly raised spot, away from low ground where water collects.
- Keep the fly tight, with guy lines staked out.
- Make sure the fly does not touch the inner tent, since contact can let moisture through.
- Open the vents to reduce condensation.
- Dry the fly fully before packing it away, to prevent mildew.
Can you use a tent without one?
On a clear, warm night, leaving the fly off lets you see the stars and improves airflow. Keep it close by, though, since the weather can change quickly and dew can soak the tent by morning.
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