The primary water-resistance comes from a TPU coating on the backside (the side that does not come into contact with food). TPU is considered to be safe and non-toxic (it is used in implantable medical devices, and is considered safe for food contact), as well as environmentally friendly (it biodegrades after 3-5 years in soil).
The lining also has a bio-based, PFC/PFAS-free water-repellant, that is food-safe, and sustainable. It is approved by both Bluesign and OEKO-TEX - both companies that guarantee the highest level of security for consumers. They test the chemical composition of textile products to ensure healthy and safe materials.