Thank you very much, Richard.
The results are bitter-sweet, not as bad as they could have been, but not so good as I'd hoped.
Your comments about abrasion resistance relate somewhat to Colin's concerns about it also. I suppose a basic issue is whether silcoated materials per se are suitable for pack material. I have some 3.8 oz double ripstop from Rockywoods – it is still offered there I think – that is PU coated. But I'm doubtful if the HH is much over 2Kmm either, and it is heavier. Also have some 200 denier ripstop from Seattle Fabrics that has a heavy 1.5 oz PU coat and is around 4.5 oz.
My chief attraction to the nylon is the lesser damage it suffers from stitching and pressure on stitching than mylar or PET laminates, not to mention that 6,6 nylon is a fairly sturdy material in its own right.
So my inclination is to go ahead and build a pack from one of the gray/silver materials. All these materials are obtained by a person who picks up remnants from balloon makers, so it is quite possible that some of it gets discarded due to defects, which might well be the case with the blue.
It will be interesting to see how the pack survives the elements, primarily in terms of water and abrasion resistance compared to the light PU coated 4 oz spectra gridstop used in the past. If I can get the pack done this winter as planned, there should be something to report here in Fall 2014. Most of the focus and work on the project has been on developing an hourglass frame design from Easton 340 tube and elbows sold by Quest Outfitters; so worst case, another pack could be built for the frame from the Seattle Fabrics offering to achieve greater abrasion resistance and WP, but with added weight.
Thank you again. I'm hopeful others will benefit from this info also.