In order to keep our customers comfortable and itch-free, we utilize 100% cotton thread on our Natural colored items. However, for the colored ones, we make use of a premium-quality, core-spun thread that combines a high-tenacity polyester filament core with a 100% cotton cover.  Although it's a cotton-wrapped polyester core thread, the actual percentage of polyester core thread in our colored items is only a maximum of 1% per garment. If you're wondering about the quality and safety of our 100% cotton thread,  please see OEKO-TEX STANDARD 100 Certification. For our poly-cotton spun thread, you may also view its certification here.