I was looked at my Xpac grid of fabric and Dimension Polyant manufactures Xpac High altitude Tent fabric with advanced UV protect, it is 40 denier polyester.It has sail cloth technology with Ti02 coating and weigh 2.3 oz. per yard.
I check my list of what they have for sale that they sent me about month and half a go they had VF31 for sale in the color grey for$9.15 yard and Vf 31 orange $9.55 yard.
I would think this would work for what you need it formulated for tents at high altitude base camp like Mt Everest expeditions.
To purchase the fabric call Dimension Polyant ask for the consumer sales to purchase fabric ask them if the have any in stock. Ph# 860-928-8300
I also found some white 1.9oz polyester ripstop color white on sale for $7.25 yard at seattle fabric while the supply last.