Samsara Bike Club t-shirts are available to anyone, you don't need to be a member of the club. They are made from a breathable sports material. I have sample sizes you can try on if you attend the Saturday club.
I have to get them printed in batches, so you may have to wait a few weeks to you get your t shirt. I will make the next order before the end of May and notify you by email when they arrive.