It's late at night. You're lying in your tent and it's just started pouring down. ‘Umm, is this tent waterproof?’ Having a waterproof tent is essential but how do I know if a tent is waterproof?
There are some important things to know when choosing a tent and making sure it's waterproof ...
Tent fabric ratings - Most tents are made using polyester fabric which is not waterproof. So a PU (Polyurethane) coating(s) is applied to provide ‘waterproofness’. The hydrostatic head is a measurement of how waterproof the fabric is, and is measured in mm, usually ranging from 800mm up to 10,000mm. There’s no internationally recognised standard of what specific rating ‘waterproof’ is, but 1500mm is widely accepted as being the minimum to be deemed waterproof and able to handle most rain conditions. A tent with a 1500mm rated fly means a 1500mm high column of water can be held up against the fabric for one minute before a drop of water seeps through.
Generally, the higher the mm rating, the higher the ‘waterproofness’ of the tent. But depending on your needs and use you probably don’t require the highest mm ratings, as more coatings mean more unnecessary weight, higher costs and chemicals in the coating that can also weaken the fabric.
With nylon tents, silicone coatings are often used to improve the fabric’s waterproof properties and strength referred to as silnylon. Silicone coatings are very smooth and taped seams will not stick to them and so buyers may have to apply a seam sealant by hand. To get around this manufacturers may apply a silicone coating on the outside of the nylon fly and a PU coating on the inner side, allowing taped seams to be applied to seal the stitching.
Canvas fabric works in a different way to keep you dry and so mm ratings are much lower. Canvas is breathable and relies on the cotton swelling when wet to close the gaps between the threads and stop the fabric from leaking. Polycotton (a blend or canvas and polyester) and canvas tents need to be ‘seasoned’ first before use (repeated wetting and drying of the fabric). Canvas weave tightens up and becomes very waterproof and is highly regarded by a lot of campers.
Seams and stitching - Check where the tent material has been stitched together. A transparent ‘tape’ that has been applied using heat should cover all stitched seams and places where additional items like toggles or attachment points have been sewn into the fabric.
Floors and Groundsheets (and Footprints) - A tent floor needs to be hardy. We stand, sit, lie on it and push it into ground that may be damp or wet for long periods of time. Polyester and Nylon floors are often thicker and have higher mm ratings ranging from 1500mm to 10,000mm to meet the greater wear and tear. Floors can be also made of waterproof non breathable PE (polyethelene) and heavy duty PVC.
Bathtub floors are common, with sides that turn up at the edges minimising chances of water entering your tent. If tent floors have seams also check that they are sealed.
The use of footprints with tents is debated. Some argue that the added protection of another layer between the ground and your tent floor will reduce moisture rising from below and also protect you tent floor form rough surfaces. On the other hand others say they are unnecessary, add extra weight and in rain will collect water and pool it directly under your tent floor.
Zips - Zips are a potential place for rain to come in. Make sure they are protected from the rain with flaps to keep water way. Power cable entry zips should also be protected from the rain.
Door and windows - The design of some tents makes it easier to enter and exit without rain falling directly into the tent as soon as you open the door. Make sure that tent doors and windows have proper coverage and flaps to prevent possible leakage.
Storm flaps and skirts - Some tents have fabric flaps or skirts that extend from the side of the tent out and away from the groundsheet which helps direct water away from the tent.
I personally would probably only look at a tent that has taped seams, is of a good design and has at least a 2000mm fly and 3000mm floor. But hiking tents, tramping tents, family tents, ultralight tents, and casual camping tents all have different purposes, priorities and requirements. If you need any help working out what waterproof tent is right for you then just ask us here and we’ll be happy to answer any questions you might have.