It seems as if there are alot of materials that are perceived as "better" without sufficient data to back up the claims. I am not going to list them all, but one material in general (Xpac) really interests me so I would like to hear more people's perception on why this material is "better" then a more conventional woven material. For example lets use the VX21 vs. 400/420d Packcloth since they are a comparable weight.
The VX21 Xpac has a 200d Oxford face, Black Polyester X Ply at 22 degree's, .025 mil PET film, 50 denier polyester taffeta, a dwr and by my scale weighs 6.7oz sy.
The 400/420D Packcloth has a 1oz PU coating, a dwr and by my scale weighs 6.0oz sy.
Here are some things I do know. XPac is easier to work with since it has zero stretch, A backpack made out of Xpac has more structure making packing and unpacking easier, Since the material uses a white taffeta on the inside its much easier to find things in a pack, the material is highly water resistant, The X ply yarns really create a nice tear resistant fabric.
With that said, the Xpac is heavier, more expensive, and might not be as abrasion resistant as a comparable weight material (i.e Packcloth).. The first two negatives are a given but alot of people are going to disagree with the abrasion claims. These numbers came from DP.. In a lab, their VX42 400d packcloth has roughly 10X the abrasion resistance as their VX21 200d oxford. Taber Abrasion, ASTM 3884, H-18 Wheels, 1000g load> 200d VX21 50 Cycles, 400d VX42 570 Cycles.. Now I realize I am comparing apples to oranges, but the only difference in VX21 and VX42 is the face material (200d vs 400d) so is pretty obvious the packcloth face is more abrasion resistant then the oxford face so the VX21 is going to be less abrasion resistant then a standard woven Packcloth.
Since abrasion resistance is a big deal in a pack, I look forward to people's thoughts..
P.S. I have a commercial interest in this topic.