Tent Fabrics – an objective summary of the 21st century options

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Having written a comprehensive review of tent design, several people asked if I could write something similar about tent fabrics. This was a subject, at the outset, which I knew rather less about. However having spend eight years as a material scientist working with powders I have been pleasantly surprised how this skill set has transferred and been valuable when reading around the topic of tent fabrics. As with my original article my aim is to present the facts objectively and without bias. I am simply a hill walking & backpacking enthusiast of long standing with a background in chemical and material sciences but no professional or financial interest in the tent industry.

Definitions / Glossary

I am going to limit myself to the fabrics used with modern backpacking tents, if you want to know more about cotton canvas, this is not the article for you. Let’s start with some definitions to help you read the tent makers specifications and sift out the facts from the hype.

Denier – This is a comparative measure of the thickness of the fibres from which a fabric is made. It is the mass, in grams, of a 9000 m length of the fibre. The definition stems from the fact the 9000 m of single fibre of silk weighs one gram. If all else is equal, then the higher the denier the stronger the fabric. By definition, higher denier fabrics are heavier. But as we shall come to see, fibres made from different materials have different strengths.

Thread Count – This is the total number of threads (total of vertical and horizontal) within a square inch. Again if all else is equal, the higher the value, the stronger the fabric. Thread count is not universally quoted with tent fabrics.

Tensile strength – the force required to rip a sample when force is applied to opposing ends of the sample. This is a more useful measure than either Denier or Thread Count when comparing tent fabrics.

Specific strength – The tensile strength per unit weight of a material of the same dimensions and critically, thickness.

Ripstop – this is a fabric which periodically has a stronger fibre added into the weave with the aim that any tear be unable to propagate beyond that fibre.

ripstop

HHeadHydrostatic head (HH) – It is measured as a length, representing the maximum height of a vertical column of water that could be placed on top of the fabric before water started seeping through the weave. Whilst a HH of > 3000 mm may seem extreme at the outset, remember that HH is really a measure of pressure and the pressure on a tent fabric can be increased by wind-speed on the fly, or weight applied to the groundsheet.

Coating – a second material applied to the surface of fabric to change its material properties. In the case of tent fabric this is usually something applied to make it waterproof. Whilst historical fabrics such as canvas were intrinsically water resistant, modern fabrics rely on the coatings applied to make them waterproof, both polyester and nylon fabrics are not in themselves waterproof.

Base fabrics

Today’s tents are generally made from one of three fabrics, polyester, nylon or DCF (Dyneema Composite Fabric). Each have their good and bad points. If you are looking for a lightweight backpacking tent in 2021 you will find that most are made from nylon with just a few made from DCF.

PolyesterPolyester has a lower specific strength than nylon, so to be of the same strength it needs to be thicker and thus heavier. Whilst it is slowly degraded by UV light it is less susceptible than nylon. It’s highly significant advantage is that it does not stretch (significantly) when wetted. Traditionally cheaper tents has been made from polyester as the fabric itself is cheaper, but this comes at the cost of extra weight. The main reason it is cheaper is the scale on which it is made for other applications.

Because of it’s lower specific strength the lightest polyester fabric readily available is 20 denier. By contrast, 7-10 denier nylon is common.

Screenshot_2021-01-29 Hilleberg tent materialsNylon has a higher specific strength than polyester, is more flexible / pliable and is thus easier to pack down to a small volume. However, it does stretch when wetted (Nylon 6,6 by 2.5%) and holds more water within its structure and thus gains more weight when wet than polyester. It is also slowly degraded by UV light, but in fairness today’s buyer would be more likely to change their tent because of an improvement in design than due to fabric degradation. Where UV damage is more of an issue is at high altitudes, above 5000 m, where UV light is a stronger component of the light spectrum. This can be mitigated by choosing a fabric colour which absorbs less UV light. Apparently green and brown fabrics should be preferred over red or orange.

DCFDCF, Dyneema Composite Fabric or Cuban Fibre is not strictly a fabric because it is not woven. Now I’d headed the etymologists off at the pass let me tell you what it actually is. It is a non-woven mat of UHMWPE (a type of polyethylene) sandwiched between two layers of polyester film. Typical of all composite materials it marries the qualities of two materials , the UHMWPE is a very strong but flexible fibre and the polyester film is both waterproof and water impermeable. A very similar composite material called Ultra is now being used for some tents made by Terra Nova.

The specific strength of DCF / Ultra is far higher than polyester or nylon fabrics. So for comparable strength DCF can be significantly thinner and approx. 35% lighter for the same strength. It does not stretch when wetted as it does not absorb any water at all. Thus it both dries quickly and does not get significantly heavier when wet. It does not stretch under strain either so anchor points have to be stronger as they take all the force, it is not dissipated across the body of the fabric. DCF seams are commonly bonded rather than sewn, eliminating any need for seam sealing.

So is DCF / Ultra the fabric of our dreams? That depends on your application and your budget. It is considerably more expensive that Si-nylon (200-300%) and whilst it has a very high tear strength, because of it’s nature and thickness (or the lack thereof) it is far more easily punctured than the other options. It also has a lower abrasion resistance because it is a film rather than a fabric. It can be very easily field repaired, but that is likely to be required more often than you might hope.

Fabric coating options

Both polyester and nylon need to be coated to make them waterproof, DCF does not. The same coating options exist for both.

Polyurethane (PU) coating

This is usually applied to the inside of the fabric and bonds to it’s surface. A significant benefit is that seam tape can be stuck to the PU and thus the seams can be readily sealed. PU hydrolyses with time (reacts with water to break down) and this will eventually cause it to delaminate and fail. That said my Si coated / PU lined Solar 2 flysheet lasted 15 years before it started to fail.

Silicone coating

Silicone coatings soak into the weave of the fabric and actually increase it’s strength. This is true for both polyester and nylon. They are far more chemically stable than PU and thus have a greater lifetime. The only downside is that because of their ‘slippery’ nature they cannot accept seam tape*. Brush-on seam sealant is available but is usually expected to be applied by the buyer rather than the manufacturer. Some tent manufactures overcome the seam issue by designing the seam positions to reduce the water loading onto the seam. Hilleberg uses specially cooled needles for flysheet seam sewing which leads to holes small enough not to allow water to pass through them.

*Thanks to recent development work at Vaude a way to apply seam tape to Si-Nylon has been developed, but is currently (Feb-20) unique to them.  In parallel with this they have also started offering bonded rather than stitched seams on a couple of their flysheets which they describe as seamless.  A bonded seam does not, in theory require secondary sealing it should be fundamentally water tight.

Silicone coatings are more expensive than PU as you might imagine, and designing out the seam issue comes also at an added cost. However, if your budget allows, silicone is the superior coating because it adds strength, allowing for lighter base fabrics and has a longer service life.

Dual coatings

Some manufacturers apply PU to the inside of the flysheet and silicone to the outside. I’ve read extensively and can see only one reason why this might be considered technically superior. That is that it allows for factory seam taping. I cannot help but think that the primary driver is cost.

Practical considerations

The groundsheet of a tent needs to be more robust that the fly and this is achieved by both higher denier fabric and the application of a greater number of layers of waterproof coating. The groundsheet does not need to have a 5-10 meter hydrostatic head for the purpose of keeping the water out, but this comes as a bonus once you’ve made your floor robust enough for it’s duty.

The inner tent fabric is something that is little discussed, but experience has taught me that it is advantageous for this to have some form of water repellent coating (DWR). A fabric that wets less easily will dry more quickly (because the water transport coefficient of a material is proportional to contact angle since you asked!) and this can be very handy if you have a damp inner tent because you have packed it next to the condensation left on your fly. I favour ‘all in one’ pitching / striking and find it takes ≤ 20 min for my inner tent to become totally dry post a re-pitch. Having reviewed the websites of a wide range of manufacturers I only found one which claims this feature. Others may offer it, but they certainly don’t shout about it. Perhaps spraying your inner tent with Nikwax Direct would be worthy of consideration?

Conclusions

So what is the best flysheet option? That depends on your planned application and your budget. When choosing a tent I would be guided primarily by design, Unless you are buying a ripped off design made in the Far East you should expect a well designed tent to have an appropriately specified materials. A strong fabric with poorly re-enforced guying points which are badly positioned will not make the most of even the best fabric. Once you have chosen the design that fits your application, then your choice of manufacturer is likely to be primarily influenced by your budget and weight target. It is an eternal truth that less is more! Some manufacturers offer different ranges of the same designs with cheaper heavier models and more expensive light-weight versions.

[] If you are fastidiously careful, want to travel very light and have very deep pockets then you might well consider DCF / Ultra as your tent fabric.

[] If you favour peace of mind and longevity then silicone coated nylon is probably for you.

[] I hope that if you are buying on a budget that this article will allow you to see the strengths & weaknesses of cheaper materials and ensure that your chosen supplier has compensated appropriately. 70D polyester in place of 40D nylon for example. Remember that the lower price is a strength if it is what makes your adventure possible.

Finally, the research behind this article suggests that there is a gap in the market for someone to develop a stronger low denier polyester fabric. There are a couple of niche manufacturers who offer 20D Si-polyester based flysheets (TrekkerTent, The Tent Lab) which may offer you the sweet-spot between weight, strength and a nice taut pitch.

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Double Pegging

Double pegging / back staking

I am indebted to Shamus McCaffery for reminding me of a technique I used when staking out the summer fete marquee’s when I was a Scout some 30+ years ago.  That is to ‘back stake’ a peg with a second peg.  He nicely demonstrated that it more the doubles the force required to pull a peg out from the ground by a simulated guy line.  A quick shake of the internet suggests that whilst this method is still common with marquee pitching it is not commonly spoken about within the backpacking community.   It’s a cheap, simple and effective solution as you just need a couple of extra generic V pegs.

It works most easily if you have a cord loop on your pegs, if you don’t then most pegs made in the last five years can have cord added.

The one thing I’d add is from recent experience is that this method isn’t just good for guys, it is also ideal for your first two peg placements when you are pitching solo in a strong wind.  Even if you don’t carry spare pegs, at this point you will have plenty.  Then, once you have most of your pegs in place the load will be shared across them and, if necessary, the initial back stakes can be removed and used elsewhere.  I wish I’d thought of this ahead of my Storm Bella test pitch, but both you (dear reader) and I will know for next time.

Soulo

Trusty Soulo at the top of Buckden Pike

Hilleberg Enan – A review

After 7 trips and a total of 12 nights of wild-camping in the hills I concluded that this twist to my love of hill walking was not just a passing phase and I could justify getting some lighter kit to enhance the experience still further. Swapping out my petrol stove for a lightweight gas stove last year was a good move and inexpensive. A lighter tent which would meet all my requirements was to be a more significant investment.

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These are my initial thoughts on the Hilleberg Enan, something which I see as a ‘Mark 2’ to the popular Akto. For those wanting to skip to the executive summary – after two ‘test nights’ it seems to be great tent for my needs:

  • Lightweight (albeit not ultralight) – 1200 g
  • Robust
  • Weatherproof
  • Flysheet first pitching
  • Good size inside, and it has just enough headroom
  • Really quick and easy to pitch on your own (kind of important for a solo tent!) even in strong winds.

Update : One year and 14 nights on, I’ve now written a more detailed assessment, I’m pleased to say it simply adds to and does not disagree with my initial thoughts.

What is the space like inside?

Perfect for my needs. I am 5’ 11” and find the length of the inner tent around 6” longer than my absolute needs. If I have my feet all the way to one end, then the height over the inner tent above my face when sleeping is not claustrophobic. If you are much above 6’ that might be different. I can sit up at the highest point of the tent with about 1” above my head in my normal posture. If I sit bolt upright my head brushes the inner. The Terra Nova Laser is 2 cm taller.

There is space for a set of clothes, book, torch etc in the vertex next to the middle of my sleeping mat. Plenty for 1-2 night stop. The porch is excellent with plenty of room for my 55 L pack, boots and waterproofs in the fixed fly half and enough space to cook within the openable section. One great addition would be if I could figure a way to attach the door corner to a walking pole to stretch it out like a tarp. This is a nice feature of some Nordisk tents. I suspect something could be fashioned from a short length of climbing cord.

How does it handle the wind?

The Enan coped well with winds up to 40 mph in an exposed position. I have added two extra guys to the windward end for which there are fittings for this purpose. This helped make the fly tighter and provided reassurance for this life long tunnel tent sceptic. The tent flapped a bit, but the flysheet material does not ‘crinkle’ like a crisp packet. The benefits of silicone over PU I guess. I think this was probably the strongest winds to which I’d be keen to expose the tent. On reflection I do need to be aware that I’m used to using bombproof geodesic tents. That this single pole tunnel tent would best be pitched in the lea of a wall or a bank is the price to pay for the reduced weight. I reckon that’s fair enough.

How does it handle condensation?

Most Hilleberg tents are designed to be able to be used in snow with their flysheets coming right down to the ground. This reduces the ventilation between the fly and the inner tent and seems to lead to significant condensation for many people. So significant as to be ‘unworkable’ in a number of reported cases.  So, for me at least, it was time to think about the science. According to a variety of sources, and depending on body weight and environmental factors, people respire between 300 – 500 ml of water over an eight hour period of sleep. If little or none of that water escapes the tent then that could become a lot of condensation. Also as the temperature drops overnight so will the dew point of the water laden air within the tent. Thus I reasoned, if you choose to sleep in a tent whose volume is very small, you are likely to end up with a condensation problem whatever the make / shape of the tent.

So, was the Enan likely to reduce this issue to an acceptable level? On paper Hilleberg looked likely to have resolved the issue and asking around proved that it was people with problems who had published their thoughts, a good number of long-term Akto users were quietly very happy with their tents. The secret to reducing condensation is to have a good number of air changes within the space. Good air circulation is promoted by having a cross flow of air, ideally from bottom to top rather than just from left to right. This is how sash windows are designed to work.  Here Hilleberg have come up with an unusual but effective solution by including a mesh panel at both ends of the tent, the ends which should be aligned with the direction of the wind. [Also true of the Terra Nova Laser.]

Cunningly, these are steeper than vertical. Thus water from the fly will not run down them, nothing can pool on them either. Whilst wind blown rain will pass through them it is slowed down enough so that (in my experience) >>99% drops to the ground before it hits the inner tent. In my first pitch in an elevated exposed position, with winds of 40-50 mph and heavy rain I counted three drops of water on the inner tent behind the windward vent in the morning. No water actually came into the inner tent itself. There are rain covers you can put across the vents if the weather is really foul and thus is best done from outside the tent ahead of need, it’s very fiddly to do from inside the tent in the middle of the night.

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On my first test night I had both vents open until around 0500 when I shut the windward one. Things were getting a little wild outside! In the morning the inside of the fly was completely dry. However the overnight temperature was a very mild 14 C. On my second test night I shut the windward vent from the outset and devised an effective and lightweight way to keep the top of the door open despite it’s design.

This is where Hilleberg may have missed a trick. The Akto has a small rain hood over the top of the door and a second zip allowing you to have a segment of the door open, not just a slit which is practice is pretty much held closed by the tension of the flysheet. But if a 10 g clothes peg can reduce the condensation I have to carry in a damp tent by 100’s grams it’s an excellent investment. After the second night which consisted of heavy rain, 20-30 mph winds and a minimum overnight temperature of 10 C I had just the lightest layer of condensation on the flysheet, an amount that anyone would consider acceptable.

What next?

With pubs and campsites to open from 4th July, I think I have the ideal tent to walk a five day section of Wainright’s Coast to Coast. Thanks to the Enan and an upgraded sleeping bag, my kit will be down by a whole kilo on what I’ve had until now, and at 10 kg (excluding food and water) this is around half the weight which I used to carry 30 years ago.

Update : If you want to know what I think a busy year into it’s use then see my long term review here.

Time for a 21st century thermostat

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It’s ironic, a good friend and I discussed the idea of a wifi enabled thermostat around this time last year.  Just after this the Nest came to the US.  Now today in the UK there are a number of offerings.   Interestingly the cheapest I’ve found so far is the Nest at £179.  My market research told me that the price people were prepared to pay was in the £50-100 bracket.  This is what stopped our project, as we could make very little margin on this.  I’m still keen to have one myself and probably would pay up to £150 for one even though the savings would take a few years to recoup this, I’d be happy to have improved convenience.  My question today is, have you – my wide and varied readership – come across (UK available) offerings in addition to those I list below which meet my spec.

  • Totally wireless thermostat (wireless link to boiler, router and battery powered)
  • Work with a Worcester boiler.
  • Controlled via an interface which could be accessed on an Android phone, Mac or PC (web access I’d guess)
  • Good, clear simple programming that worked on a 7 day basis, with four periods per day and the option of a timed holiday over ride (i.e. the standard programme would not be lost but could be re-activated after getting home – automatically on a set day – ideally with an independently programmable option for the day of return itself.
  • Smart – learns the response of the house to the heating and also adjusts depending on the weather via data it can gather from the web (after all, it is linked to the web, so this should be possible)
  • <£150

Systems I’ve come across so far are

  1. Nest – but this is auto learning, not programmable.  It also seemed to be based on US fast response hot air heating systems and I cannot see this working with a UK gas to water CH system that takes two hours to get the house to temperature in the winter. £179
  2. Hive – this seems to be programmable to meet my spec, has the totally wireless thermostat but is in no way ‘clever’ £200
  3. Tado – works by tracking where your smart phone is. I cannot see how this would work with a household of three people and cannot see how it would know for people who regularly are close to home but don’t intend to go home, that this was your plan.  It has it’s audience, but I don’t think I’m one of them.
  4. Evohome (Honeywell) – I think this meets all my technical requirements (not 100% sure if the thermostat is battery powered though) but at a cost of £337 plus installation, well outside my limit.
  5. Inspire – not ‘clever’, battery powered but not wirelessly linked to the boiler – £125 (inside budget)
  6. Heatmiser – research ongoing – does not appear to be fully wireless – wide range at range of prices.
  7. ???  What else is out there dear reader?