Cotton varies greatly. My Maya wrap ring sling is 100% cotton, but very thick and warm. My hotslings pouch sling is 2 layers of thin cotton and great for hot days. Linen is durable and often cooler, but more expensive.
I would get linen. Most cotton weaves that you can pick up at the fabric store aren't really suitable. All cotton tablecloths can make nice ring slings though (you want something heavier than quilters cotton and ideal a fabric that doesn't have a "wrong" side).
Re: Sling Fabric
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