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. F Removable, silicone boot adds extra protection to your Hydro Flask Small boot fits 12-24 oz wide and standard mouth bottles S BPA-Free Compatible with all Standard Mouth products for ultimate versatility.