It helps to distinguish between nylon ‘stretch’ and nylon ‘sag.’ Stretch is the elastic quality that recovers its shape in a flash. Sag is the lack of tension in the fabric that results from increased cold and humidity, and allows the canopy to sag, greatly decrease the usable area, and make the occupant(s) wet. And sag does not recover until the weather warms up. We have all seen saggy tents, but usually not in the manufacturers’ photos.
It is not clear whether the 7D ‘custom’ material used by GG is like the
Rockywoods 7D, or nothing like it.
It is also not clear what the tear strengths are.
Nor do we have any aging tests on the 7D materials that show whether what begins at an acceptable level of HH holds up or not. We have seen repeated examples of ‘not’ in Richard’s tests posted on this site.
But, not sure if we have to answer all these questions before buying a shelter or ordering the material for MYOG. From .5 oz Cuben to 1.25 oz 15D nylon or polyester is a bump up of .75 oz per sq yd. Some of the tarps, as well as many tent designs, run less than about 8′ by 9′ or 8 sq. yds. That’s around a 6 oz bump-up to the weight of the whole canopy. The rest of the weight is in reinforcements, etc., which with the newer PU/SIL coatings, so long as at least one side of the fabric has the PU, can be strongly bonded on without stitching, more strongly than any of the Hysols with Cuben.
There are enough tests already posted here by Richard to show some good choices in 15D 1.1-1.2 oz (including coatings) materials. For me, the less than 6 oz weight penalty of having a much stronger shelter, more reliable in severe storms, is not significant considering the importance of shelter.
A greater concern is the amount of sag if the material is nylon, and whether a 15D polyester, with its minimal sag will hold up in severe weather. Sag tests are easy to do with plastic embroidery loops, and perhaps some can send samples of some of the better HH (after simulated aging) polyester materials to Richard to see if he can shed any light on tear strength. That would be helpful to know, as a no-sag shelter will be a lot more comfortable and a lot less trouble, but if and only if the strength is acceptable. Maybe we can make some choices without waiting 5 years.