Printful has mesh hats in their catalog. Have you already been browsing the print on demand apps in the Shopify App Store? I'm happy to search with you if you can let me know which ones you've already looked at.
I'm curious to know how far along you are with your print on demand store. Are you still in the building phase, or is the store already launched and you're adding some new products?
Sophia | Social Care @ Shopify - Was my reply helpful? Click Like to let me know! - Was your question answered? Mark it as an Accepted Solution - To learn more visit the Shopify Help Center or the Shopify Blog