Hi folks, I thought I'd chime into the fabric discussion. Bear with me :)
The biggest thing to keep in mind with all of this is that every fabric has applications, and within the design of gear (especially backpacks), success is going to come from matching an appropriate fabric to a fitting design element.
When I consider fabrics for use in packs, I generally look at four things:
1.Relative tear strength- How easy will a fabric shred when it is pulled and tugged upon. This is mostly affecting stitch hole elongation, very important for load-bearing areas, (ie suspension-systems: shoulder strap and hipbelt attachment points)
2. Abrasion resistance- How will the fabric hold up to abrasion. These needs are dependant upon design elements. A 40denier or 70denier fabric may be appropriate for an extension collar, but I generally dont want the bottom or front of my pack made solely of this stuff (unless I'm going SUL!)
3. Waterproofness- How well will a fabric resist water penetration through the fabric. (PU coatings are generally more supple, but wear off in time. Laminates (like Xpac or cuben maintain their waterproofness longer (or so we're led to believe))
4. Long term durability- how well will a fabric hold up to UV degradation, will a PU(or other coating wear off with time, etc)
Other factors like stiffness, color etc are a bit less functionally important to me as a bag designer.
The three big players for pack fabrics right now seem to be Xpac(several styles), Cuben(two hybrid variants) and the ever popular 210 Dyneema Ripstop.
"So what advantage (if any) does hybrid cuben have over Dimension Polyant fabrics"
The tensile strength per weight is FAR higher. The dyneema content of cuben is the cause of this. Dyneema being a much stronger material than nylon or polyester PER WEIGHT
For regular non-woven cuben(rarely seen in heavy-use packs), sewing is an issue because of stitch-hole elongation. This comes from the VERY loose-knit structure of dyneema thread in the material(hold a piece of cuben up to light and you can see all the individual threads).
For Hybrid cubens, the face fabric helps solve the issue with stitch hole elongation(but then is only as effective as the face fabric plus the cuben, and the lighter weight hybrids have only a 50D face fabric).
Any Dimension Polyant Xpac fabric whos name begins with "V" as in VX70, VX21 etc has a LINER of 50d polyester. That has the same denier (thickness) as the FACE fabric of the common 'lightweight' hybrid Cuben.
IMHO, it's hard to find a true workhorse fabric under 4oz/yd2. I personally don't see the lightweight cuben hybrid as a workhorse fabric. It fills a niche and thats great. But as a general use pack fabric, its abrasion resistance is too low for my liking.
Looking to the future,a new fabric that I'm excited about, and have been testing and sewing with the last 6-8 months is the new Xpac X21. It consists of a 210D nylon face, Xpac grid and a thicker .5mil (instead of .25mil) film. No 50d Scrim. Lack of scrim (most likely a wash for a 210d Fabric) creates a fabric about 25% Lighter than the common VX21 While maintaining similar tear strength(at this denier of fabric, the tear strength comes mostly from the face fabric anyway).
DP seems to be creating this option for their larger Denier fabrics(as evidenced by the new X51 also, and the soon to be restocked X33). It makes a good deal of sense to me.
All said, I'm an Xpac man myself, but I see the viability of a niche for cuben hybrid. The DyneemaX stuff is great too, but from a producers perspective, Xpac is a better value, delivering much more bang for the buck.
Kevin said:
"Not all XPAC fabrics have the inner protection film. Some do, some don't. X33 for instance does not have it and really does not need it since it is 330D Cordura."
To clarify, Kevin, I assume you're referring to the 50d polyester liner 'Scrim', not the film. I have never seen an Xpac fabric that does not have a waterproof PET(or otherwise) film.
Brendan says:
"The DP DX40/D40 could be similar if they'd just put some spectra in both parts of the weave. It's as tough as anything in one direction and the other you can tear it easily with your hands."
I'm sitting here with a piece of D40 trying my best to tear it in either direction, and it wont budge. Perhaps I'm just weak, but it wont tear easily in either direction for me. If I remember correctly, it's a 400D polyester warp/400D spectra weft plus a 600D Spectra ripstop face fabric on, a .25mil PET film and 50D polyester liner/scrim. In my little experience, that would add up to TOUGH AS NAILS. I was told DP uses polyester in the face fabric so that their laminate will stick to the fabric better.
Reminiscing, many Years ago There was a pack maker (I believe SMD) that offered a 210D Dyneema ripstop that was produced by Xpac. It was an amazing fabric. The strength of the workhorse 210D Dyneema ripstop with the waterproofness of xpac laminates (and a 50d Polyester scrim) I made my my fifth backpack out of this stuff and it lasted me nearly 7 years of hard use. Eventually the scrim fabric delaminated from the face fabric and I cannibalized it. If I had the capital to purchase 1000 yards of uncoated dyneema ripstop and have Xpac laminate it for me, I'd be all over it.
P.S.
For fun, as a very unscientific test of abrasion resistance you can do at home: scrape a rough rock across the face of a fabric it until you put a hole in it. Try with 50Denier, 70 Denier 150 Denier 210Denier fabrics etc. You will get a general idea of relative abrasion resistance. Cuben(sub 2oz) without a face fabric SHREDS NEARLY RIGHT AWAY(as does silnylon, TX34 etc)