How Waterproof Does a Lightweight Tent Need to be?

You've been researching hiking tents and you keep reading about waterhead ratings and seeing numbers like 1,500mm and 5,000mm in the description. But what exactly is a waterhead rating, and what do these numbers mean?

Lets take an in-depth look into what a waterhead measurement means, how they test it, and how much you really need.

photo: Wilderness Equipment Space 1 | Snowy Mountains NSW

Waterhead Testing

"Waterhead" testing (or "Hydrostatic" testing) is the method by which the waterproofness of a material is determined. 
Essentially, a measuring tube is placed vertically on a sample of cloth and water is then added to the measuring tube until the weight of the water (or pressure) is enough to push moisture through the material. 

The height of the water in the tube is its "waterhead rating". (Also known as "Hydrostatic Head") 

MSR Suter Tester - This machine is used to test waterhead ratings.


Tent Fly's

Tent fly’s do not need as high of a rating as tent floors do because falling rain does not exert as much pressure as somebody sitting, kneeling or lying on a floor. (This is why waterproof jackets and pants often have 10,000mm of Hydrostatic Head)
A tent fly also doesn’t generally get subjected to as much abrasive punishment as a floor does.
For a fly, 1,500mm Hydrostatic Head (HH) is considered sufficient to withstand the pressure of driven rain and most tent makers have tent fly’s ranging from 1,500mm to 5,000mm (sometimes even higher).

Lighter ratings can still be waterproof, but come with some compromise in strength, and a lower margin for error. 

Generally speaking, this is done to conserve weight as higher HH material will have usually be thicker and therefore heavier.


Tent Floors

Tent floors are a bit more complicated. Kneeling or sitting applies between approx. 16-20 psi which is roughly equivalent to between 11,000-14,000mm of Hydrostatic Head. 
This doesn’t mean that all tents need a 14,000mm HH floor. The somewhat porous nature of most materials under the tent floor (soil, grass etc.) allows the moisture in it to retreat from the point of pressure. A bit like when walking on wet sand and you can see the water move away from your foot. Because of this, a lower waterhead is often adequate.

The camp site selected can also play a part in what floor type you need, if the area you choose has pooling water then a higher HH will be required

A quick look at the respected BritishEuropeanScandinavianAustralian and New Zealand tent brands see most floors rated between 5,000 – 10,000mm with some up to 20,000mm+. 
There are a few exceptions, being specialist ultra-lights around 2,000mm however the assumption is that these ultra-light tents won't be used in extremely poor conditions. The marketing usually infers that they are for specialist use such as adventure racing etc.

Some well-known brands have prioritised very light floors to keep the overall weight of the tent to a minimum and the marketing leverage to a maximum. Some of these average 2,000mm or less on the floors. These lightweight tents are good for moderate conditions but may be unsuitable for when the weather turns a bit serious. These often require the use of an additional piece of fabric called a “footprint” to protect their more delicate floors. 

No one wants to carry more than they need to, so a realistic appraisal of your expected camping environments will help make decisions a bit easier.

photo: Mont Moondance 2 | Walls of Jerusalem NP, Tasmania


Types of usage

  1. REGULAR HEAVY USE

A week or two in South West Tasmania or the South Island of New Zealand etc can regularly provide harsh conditions with torrential, horizontal rain and frigid winds. On more remote and extended walks this can continue for days on end and a healthy factor of safety in the floor and fly counts for much more than the saving of a few hundred grams in weight.
An icy puddle or stream under a tent feels a lot less threatening with a 10,000mm sealed tub floor whereas a 2,000mm floor may do the job but there will be far less margin for error. Also, extended, remote walks can be rough on gear as well as being wet, so the extra abrasion and puncture resistance of the heavier floors give more security in this regard as well.. 

Failure of equipment is not desirable on these types of expeditions.

The walker who takes part in these more remote activities on a regular basis will usually be prioritising toughness and reliability in a tent as much as lightness. Typically, they will want a tent able to withstand strong winds and heavy rain. (we’re addressing materials here, but structure is equally important.)

We would recommend a tent with a strong fly material of at least 3,000mm waterhead and a seam sealed tub floor with a water head of at least 5,000mm.

The pole structure of the tent should also be considered. (see separate post on choosing a hiking tent) 

Most high-quality tents in this realm will weigh between 1.8kg to 4kg depending on materials, size, structure and the desired factor of safety.

  1. LESS REGULAR OR LIGHT USE

Most of us are time poor so our tents are primarily for overnighters and weekends, with the occasional multi-day track walk. 
With modern technology we can get very accurate weather forecasting and it could be said, that whilst light showers often get tolerated, full on heavy weather is much more avoidable than in days gone by. We often just re-schedule for when the weather is fine and get on with life. 
Tents are mostly set up on semi-comfortable bits of established ground and aren't subjected to more than the odd rain shower.

Manufacturers know that this is the bulk of their business. A large proportion of users can be served very well by tents that focus more on lightness and less on overall toughness. 
Fly material with a 2,000mm waterhead or less, and floors of around 2,000mm can be combined with clever pole configurations to create comfortable two person tents weighing in at 1.4kg to 2.2kg!
If looked after, this gear will still give great service and let you get out in the bush carrying less than ever. That's gotta be good!


photo: MSR Mutha Hubba | Clear Point, South Coast NSW


Footprints / Ground Sheets

With the introduction of very lightweight floors some years ago, many brands have felt inclined to 'cover' themselves somewhat by recommending the use of a footprint (groundsheet) with which you can 'protect your investment'. 
Some are now including them in the buy price of the tent, (and indeed it's rumoured that some warranties are voided if the "footprint" is not used). however, most of them require you to purchase the footprint separately and don't include it in the advertised weight of the tent. 
Footprints will reduce the wear on the floor but can pool water between the footprint and the floor in heavy conditions. 
In theory, you can leave these footprints at home if you need to go ultra-light and save a few grams.

Please note that whilst it is prudent for the long-term protection of your tent floor to use a "footprint", it is by no means obligatory unless the floor is made from very light materials (usually with low waterheads). These need a footprint to protect them. The majority of high-quality tents are designed to not require additional protection, so only make 'optional' footprints as a prudent back up, and to satisfy the growing misconception that a "footprint" should be part of every tent purchase.

Marmot Limelight | Overland Track, Tasmania


Seam Sealing

This is an important process in the waterproofing of tents. Most brands will seal the seams on the tents with either a seam tape or seam sealer, but not all brands do. Some well-respected brands don't seal the seams on their tents, so you will have buy a tube of seam sealer and to do it yourself.
This isn't necessarily a bad thing, it is just something to be aware of when buying a new tent, as you don't want to get caught out!

A Silicone or Urethane (PU) based sealer, painted into the stitching has a better ability to penetrate, flex and stretch than tape does. 
Siliconised Nylon (Sil-Nylon) materials are particularly difficult to stick seam tape to, so most Sil-Nylon fly's will need a special silicon sealer applied to their stitching. A lot of well-known brands won't seal these seams in the factory as there isn't a machine to speed the process, whereas tent fly's made from other materials like polyester can be sealed with seam tape by a seam sealing machine.
If a Sil-Nylon fly is coated on the inside with urethane then seam tape will often be applied to the stitching to where the holes from sewing are present as it will easily stick to that coated surface.

The machine used by Mont to seam seal their tents. 


Trail Weight vs Packed Weight

Another piece of terminology to be aware of is the difference between trail and packed weight as depending on which is listed by a particular brand, you may not be comparing apples with apples.

Packed weight refers to the complete weight of the tent when purchased. This includes everything such as poles, pegs, guy ropes, fly and tent.

Alternatively trail weight can mean slightly different things from different manufacturers however generally speaking refers to the weight of the inner tent, fly and poles. 


Final Thoughts

Understanding the thinking behind manufacturers designs and ratings will hopefully assist you in making the best decision for your needs when choosing your next tent.

Weight and pack size are certainly worth considering but are by no means all you should consider.

At Outdoors and Beyond, we pride ourselves on having the knowledge and experience to assist you in making a decision and look forward to hearing from you.


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