Hey Dan,
"Is there a reason to prefer a nylon/cuben sandwich over using one layer of (presumably thicker) nylon?"
Let me start out by saying we have tested and talked to a lot of people who have been using ultralight packs and the biggest issue that most of these packs have is that they fall apart either at the shoulder pad seam or at the hip belt seam or the fabrics are just to light for any kind of long term use. HMG loves a challenge, it's one of the reasons we do what we do in the outdoors. Given that, we set out to make the lightest most durable ultralight pack available. We built a ton of packs out of all kinds of materials and did everything we could to bring them to the point of failure. Once we know something failed we can start reinforcing, look at it again and reinforce some more if necessary. This is where the cuben comes in. The spectra fibers in the fabrics we use really add a tremendous amount of strength with out all the weight. We have tried making packs out of regular old cuben fiber but the weights of cuben needed to make a durable pack makes the pack very stiff and boardy, not to mention a little unsightly in my eyes. So what we have done was to use a lighter weight cuben fiber along with a light weight nylon to make a super strong fabric that is supple enough as well as strong enough to hold up to what ever you can throw at it. Not to mention the layer of Cuben makes the fabric truly 100% waterproof which was a real advantage in our eyes and I have always disliked carrying a pack cover. Now for the nylon, it is soft while still adding a great protective barrier to the cuben as well as decreasing the potential for perforation or the postage stamp syndrome as we like to call it, which is what happens to cuben fiber when you throw a whole bunch of needle holes in one spot, ie bartacking.
There is a large learning curve and expense when working with these new laminates and composites and the team at HMG is on the forefront of developing the processes and techniques to manufacturing and working with these high tech products.
When we first started looking into the world of packs we were looking into using a pure woven spectra fabric for its strength and low weight. However, at a price of $50-75 per yard it was just too expensive, still only comes in white and isn't waterproof. This woven/cuben hybrid isn't really new, its been around for a few years we were just persistent and patience, and worked with the manufacturer to create a hybrid that is not only strong, light weight and waterproof but soft enough to make a pack out of and we can get this hybrid in colors, as you will see in in the next pack we launch. Given the cost of some of these materials, we want our products to last. There are reasons why 1000denier nylon packs are still around after 20 or 30 years of use, but there are also reasons why these materials are being used less and less in the pack industry; they are just down right too heavy. We feel that given the technology of today and what we know from the past we should be able to build a pack that is the best of both worlds, light, durable, waterproof, and supple. Try it out….we really believe you'll like it!