Why use lightweight and ultralight tents? Because a heavy tent is one of the biggest obstacles to lightweight backpacking. You have to cut the weight of the “big three" (shelter, backpack and sleeping bag) to really go light. How do you choose one, though? Start by asking yourself the following questions:
1. Are you claustrophobic? Some ultralight tent designs are really just fancy bivy sacks. For those who hate tight squeezes, it will be like sleeping in a coffin.
2. How tall are you? If the length of the tent is only a few inches more than your height, you'll be touching the walls. This probably means getting wet from the condensation on them.
3. What do you do in a tent? If you just sleep, total floor and head space are not important. If you normally play cards with friends for hours, you'll need a design that allows for that.
4. Do you backpack in bad weather often? If all you plan to do is camp on nice summer nights, you can just look at the cheapest lightweight tents, and worry less about quality.
5. How much have you budgetted for a tent? More money equals a lighter tent, but if you can't get it light enough on your budget, you may want to consider going even lighter - and cheaper - with a tarp shelter.
6. Which is more important to you, fast set-up or lightest weight? Hopefully you'll find a tent with the right balance, but keep your preference in mind when shopping.
More About Lightweight Tents
Single-layer tents (without a rain-fly) will usually have more condensation inside. This is true of even those that claim to be waterproof and breathable. It is less of a problem with the newer designs that have a lot of screen/ventilation area, because air circulation is as important as “breathable" material. These materials just don't breath that well anyhow.
Test your tent. It's no fun spending 20 minutes setting up a complicated tent in the rain. Also, it can be worse than inconvenient to tear seams because of a design that stretches everything so tight you have to fight with it. Try the tent in your yard or living room, before you head into the wilderness. That way you can return it if it won't work for you.
There is only one totally enclosed 2-person ultralight tent that I know of under 3 pounds. It's a single layer, but the forward sloping door allows for a large screen area, to keep air-flow at a maximum. This keeps condensation to a minimum.
There are “floorless" tents, which are specially cut tarps which typically use your trekking poles for support. One of the lightest of these is a three-person design that weighs less than 2 pounds. I haven't tried it, but it gets good reviews, and it is in the weight range I like for ultralight tents. You have to bring a groundsheet with this type, so figure that weight into the decision.
Unfortunately, I've discovered the hard way - four tents and counting - that you tend to get what you pay for with lightweight tents. That's one of the reasons I backpack with a tarp.
Steve Gillman is a long-time backpacker, and advocate of lightweight backpacking. His advice, stories and tent recommendations can be found at http://www.TheUltralightBackpackingSite.com