Ymmv, but for on deck
stowage, I prefer Sunbrella, in dark colors. You can sometimes find coated UV resistant fabrics (they are not inexpensive), but generally speaking, the coating comes off and sheds after a while. The Sunbrella gives you the UV protection you need.
Make sure you cover the zippers with flaps. Even the YKK #10s eventually quit working after UV exposure, unless you keep them covered. Got about 15 years on the last ones, before we bought this boat
You can also make the bottom part of the sailbag out of pvc mesh (like the shade material "Breezeway"), so the water
drains out freely. A little thought goes a long way to getting what will work
for you in your particular situation.
As to your specific question, talk to someone who makes sailbags, dodgers, sail covers, etc., if someone here can't find the name of it for you.