Tents and TarpTents
In recent years a market has been created that caters for the Ultralight camper who also wants a little bit of comfort on the trail for the harsher weather conditions. In the USA this has been driven by some of the very long through hiking trails such as the Pacific Coast Trail and the work of probably three men - Ray Jardine, Ryan Jordan and Henry Shires. In the UK it has been probably driven by the KIMM (now OMM).
These four sources have probably pushed the boundaries of what a usable shelter actually means and in the process removed years of 'features' that have been needlessly added to tents and also encouraged the use of lighter rather than cheaper fabrics. Even in the 1950's they were using Silk for expedition tents when weight was critical.
This section is focussed purely on the ultralight (and comfortable shelter options).
In the USA there is now a big movement towards TarpTents - as a compromise between a tent and a tarp. Their big advantage over conventional tents is that they are much lighter for the volume that is enclosed.
The leader in this particular field is probably Henry Shires at Tarptent. He produces Tarptents that weigh between 700g and 1Kg for a complete 1 or 2 man tent.
The fundamental design concept behind the Tarptent is basically to take a shaped tarp, add a beak at both ends and then seal off both ends behind the beak using some nauseam/midge netting. The lightest designs have no bathtub floor and so must be used with a groundsheet.
For the Tarptents that do have a sewn-in groundsheet Henry has done a very clever trick of adding several inches of mesh along the entire edge of the groundsheet. This results in excellent ventilation.
The latest solo incarnation is the Contrail which effectively offers the Solo backpacker a spacious tent that weighs in at under 700g. That really is an incredible weight for a fully operational tent that costs $200.
Even in the UK this is unlikely to be an issue. The 'secret' to preventing condensation is to design in sufficient airflow so that moist air is carried away. Tarps do not suffer from condensation simply because the airflow is so good. The worst amount of condensation that I have ever had when using a tarp is to have it feel slightly clammy to the touch.
3 or 4 Season use?
Tarptents tend to be very well ventilated. In English that means they are draughty - slightly less so than a tarp, but still draughty.
You could use a tarp or a Tarptent in the winter but that does mean that you would need to use a warmer sleeping bag. For the extra weight of the sleeping bag you could just as easily buy a fully enclosed tent. It's your call.
Personally, I think that for all but winter use that people who are currently using tarps or bevy bags would do well to consider the extra comfort that a TarpTent could bring.
Is it a Tent or a Tarp?That is a philosophy question. I think it is more tent-like than tarp-like. I personally think I would just call the thing a single-skin tent. My argument for this would be that whereas a tarp can be pitched using a large number of configurations a tent can only be pitched in one configuration.
If we move away a little from the Tarptents and replace the mesh and beaks with 'proper' doors then what you now have is a single-skin tent which will be light in weight and probably quite prone to condensation - unless you use breathable fabrics. If you cannot live with a single-skin tent then for a little extra weight you can have a conventional twin-skin tent.
Single-skin Tents (not breathable)
There are very few of these that are commercially available such as the Coleman Raid 2 which is a 980g 2-man single-skin tent. There is a very good reason for this - designing the tent to minimise condensation and still maximise warmth is a total bitch.
My first attempt at a single-skin tent had almost no ventilation. The result was a wonderfully warm tent with it's very own waterfall on the interior walls. The mark 2 had plenty of well-placed ventilation. The result is very little condensation but a much cooler tent.
A cheap way to address the ventilation. issue is of course to not bother with a sewn-in groundsheet.
Gore-Tex Single-Skin Tents (breathable)
This is the standard method of trying to address the condensation issue. In reality it only half-works, some condensation will still form on the inner surface of the Gore-Tex although less so with the latest gas permeable fabrics. The net result is that you have a single-skin tent that works much better but weighs a lot more.
Gore-Tex tents tend to be very small to compensate for the extra fabric weight. To put this into perspective a Gore-Tex type 3-layer breathable fabric will weigh around 180gsm (grammes per square metre) and 2oz PU-coated Ripstop nylon or even SilNylon will weigh in at 70gsm or less.
Now, given that Gore-Tex weighs about 3x as much as waterproofed nylon it is only going to enclose about 2/3 of the same volume for the same weight. In the real world this means that the lightest single-pole hooped bivy bag you can buy is the Rab Ridge Raider which at 730g is still heavier than the Contrail Tarptent which offers much more space.
In some senses it is not fair to compare Gore-Tex bivy bags with lightweight tents. They are completely different beasts. A Gore-Tex bivy bag is really designed for extreme mountain conditions. In particular for wind and weather that would flatten a tent. The only reason that most people buy a bivy bag is to save weight over a cheap tent. That is no longer necessary.
Single-Skin tents almost always suffer from condensation. The elegant approach to solve this is to add a breathable inner tent. The condensation is still present - but on the outer skin where it cannot be touched.
For most people most of the time a double-skin tent is the ideal solution to their camping needs. The only problem is that the weight of those two skins can add up. In practice the lightest 4-season solo tent is going to be around 1.5-2Kg (e.g. The Hilleberg Akto).
For 3-season tents the current state-of the art for solo tents is probably the Terra Nova Laser Competition which has a max weight of 940g and a min weight of 860g. The closest competitor to this is probably the Mountain Equipment Helium AR Ultralite which has a max weight of 1140g for the Solo and 1455g for the two-man version.
In order to produce a tent with two skins that is this light then obviously some serious compromises have been made on the choice of fabric and poles. The tents will withstand most things that you can reasonably expect to throw at them in 3-season weather but they may not cope with storm-force winds.
However, for most people, especially a pair of hikers then an ultralight tent would probably be ideal. For a really tough tent the Hilleberg Akto or the Mountain Equipment Dragonfly would be both good choices - at the cost of extra weight.
All of these modern tents still struggle to compete with my old Saunders backpacker tent which was a 2-man tent weighing 1.5Kg. It achieved this by using light fabrics and having a low internal headroom. The more modern tents use even lighter fabrics and 'spend' it on greater internal space.
There are no easy conclusions really. With a per-person budget of 1Kg or even 1.5Kg you can buy a tent, a tarptent or a bivy bag that will meet your needs. If your weight budget is 750g then your choice narrows to a simple bivy bag, a Tarptent or even a tarp with groundsheet.
A final ultralight option that has not been discussed here is a very small tarp (150-300g) with a pertex bivy bag (200-350g) which would be lighter than anything talked about here - but a lot less comfortable.