What Luke said. He’s worked with this far more than I have. Although I have seen some break down of the waterproof layer. Read on.
Xpac has a bewildering array of fabrics. Fully understanding the line-up took me some homework. The stuff I write below is in itself a mouthful, if unfamiliar with DP Xpac.
The number denotes the denier. 07 =Â 70d, 21 =Â 210d and so on. There’s exceptions and further confusion, off course. X51, for instance is 500d x1000d.
Popular these days is X21. It’s part of the Xpac laminates without a protective inner layer of taffeta, i.e. the inside is shiny with the waterproof membrane fully exposed. This saves substantial weight.
The burlier taffeta backed version of X21 is called VX21. The weight difference is from 4.4 oz/yd to 6.0 oz/yd.
We made a pack with alternating panels of VX21 and X21 near the drawcord top. It’s a daypack and thus seen weekly use since summer 2016. The taffeta backed VX is fine, the lighter X is showing deterioration of the waterproof layer.
VX07, which the OP specifically asks about, is made with a very light 70d face fabric, yet weighs 4.8 oz/yd, or more than the far tougher 210d X21. This is due to the interior taffeta layer protecting the waterproof component.
Based on our experience with the MYOG pack mentioned, and using various Xpac bike packing bags since 2011, VX07 will stay waterproof longer than X21, but only if exposure to abrasion is kept to an absolute minimum.
Here’s a chart from 2015 that is still current I think:
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