Colorful protection.Make your Hydro Flask your own with a colorful, durable silicone Flex Boot. Customize your look and protect against bumps and dings. Small boot fits 12-24 oz wide and standard mouth bottles. Medium boot fits 32 and 40 oz wide mouth bottles. Product Benefits Removable, silicone boot adds extra protection to your Hydro Flask Small boot fits 12-24 oz wide and standard mouth bottles Medium boot fits 32 and 40 oz wide mouth bottles Medium boot is not compatible with 32 oz Lightweight Wide Mouth Trail Series bottles BPA-Free Lifetime Warranty