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How Much Lighter are Lightweight Backpacks?The backpack is part of the trio known as the the 'Big Three'. Together with the Sleeping Bag and the Tent, it's one of the three heaviest things you'll carry while backpacking. For that reason, considering lightweight backpacks is important if you want to practice lightweight backpacking.
And there is quite a difference in weights when it comes to backpacks, as can be seen over at the list of backpacks. Consider the Black Diamond Demon backpack. It's a 34 Liter backpack that weighs in at 1230 grams, or 2.7 pounds. The ULA Equipment CDT backpack though, another 34 Liter backpack, weighs just 481 grams, or 1.1 pounds.....
- Black Diamond Demon - 1230 / 2.7 pounds
- ULA Equipment CDT - 481 / 1.1 pounds
The Features of Light BackpacksThere are a few features that are fairly common among the lightest backpacks.
- Frameless Backpacks - Most people consider an internal frame to be one of the essential features of a backpack. And the way most people go backpacking, a frame really is necessary. Generally, when you get above a total backpack weight of 25 or 30 pounds, a frame is the only thing that's going to give your backpack the rigidity it needs to be carried comfortably. But if you're practicing lightweight backpacking and your pack weighs less than that, a frame isn't necessary, and you can consider frameless backpacks. Taking out the frame, it should be noted, is one of the best ways to lighten your backpack. (You can compare frameless backpacks and internal frame backpacks at the list of backpacks.)
- Lightweight Materials - A great deal of the weight savings seen in light backpacks come from the manufacturer's choice of material. Cuben Fiber (seen on many ZPacks products), for instance, is an extremely lightweight fabric. The drawback is that it is gradually degraded by sunlight, and rips relatively easily, so long term, it's not a great choice (Though the prices of most cuben fiber packpacks are low, so replacing is no great loss). But that doesn't mean you need the heavy duty stuff that many manufacturers use either. A popular middle-ground fabric is Dyneema. Dyneema backpacks are strong, don't rip easily, and are lightweight. ULA Equipment is a popular manufacturer of Dyneema backpacks, but you'll find a lot of the light backpack manufacturers use it.
- No Lid - Many ultralight backpacks forgo the lid and have what is called a roll top closure (The ULA Equipment Circuit for instance). While not as weather proof as the more traditional lid, you'll probably be using a bag liner anyway (garbage bags work nicely) so it's kind of a moot point.
- Top Access Backpacks - Many backpacks have a sleeping bag compartment at the bottom of the bag, from which you can also sometimes access whatever's at the bottom of the main compartment. Some backpacks also have zippers running down the side of the backpack or even the front, to allow you access to the main compartment without having to dig. But zippers are heavy, and if you're bringing so much stuff that you need all sorts of access ports, you're probably bringing too much. Most lightweight backpacks forgo these additional access ports, though not all (The ULA Equipment Camino is a front loading backpack).
Drawbacks of Light BackpacksThere aren't too many drawbacks with using the lightest backpacks. Some people will be squeamish with not having an internal frame, but if you're not carrying that much a frame is nothing but extra weight. It should also be said that some light backpack manufacturers sell frames as an option on their backpacks (ZPacks and Six Moon Designs for instance), and there are some very light backpacks with frames on the market (see the list of backpacks to find them)
The only other problem you might encounter with ultralight backpacks is the chance of a rip. This will be more or less of a problem depending on the fabric that your backpack is made from, but unless you're doing some serious bush whacking or choose something like cuben fiber, you don't have much to worry about.