I use polyester thread, Gutermann to be specific. Coats and Clark has a polyester called Outdoor Living which would be good too.

Curious tho, if someone is making them for you, shouldn't they already have thread and know which to use?

Shadylady and CT - thank you so much for responding and providing this information. I really appreciate it. The person doing the sewing is not a trades person, but a family friend who does a lot of sewing and always requests a sewing project when she and her family stay at our beach house. Not sure why she hasn't responded to me about the thread but she's traveling now and I can't reach her. I still have some time before she comes. Thanks again for responding to my first post on the sewing forum!

Nylon breaks down over time, sooner than polyester. Use a thread with a smaller number gauge, which is heavier, like a 25 rather than a 100.

Susan, this is excellent information. Good to know about the gauge. Thank you so much. Here is a pic of my fabrics. Solid for the seat cushions and patterned for the wedge bolsters.

Sunbrella recommends this thread: Sunstop thread

Not sure how much you want to spend, it's pricey.

Shadylady thank you for that link, it was so helpful. I’d been to the sailrite website before but got overwhelmed with their threads! From your link I was able to determine needle size and thread size and gain information I never knew I needed. There was even a link to a detailed thread comparison chart! I’ll search locally for thread and if I can’t find something near equivalent I’ll order from sailrite. Thanks again.