🌟Medium/3.56inch diameter--It was designed for Hydro Flask Water Bottles 32oz 40oz wide mouth. Extensively compatible with Owala boot Freesip/Flip/Twist 40OZ and other brand water bottle with bottom diameter 3.56inch.BUT THIS MEDIUM(3.56inch diameter) BOOT IS NOT compatible with 32 oz or 40 oz Lightweight Wide Mouth Trail Series bottles 🌟UNIQUE DESIGN - Try more colors/Designs and create a bright new looking for your favourite flask. Warning: silicone boot only, flask water bottle is excluded. 🌟Soft silicone material - Made of high quality food grade silicone material, it is safe, soft and a bit stretchable, easy to put on and take off for daily use 🌟PORTABLE TO CARRY – Reusable, durable, foldable and dishwasher safe. Our sleeve can withstand stretching, folding, and anything life throws at it 😊SATISFACTION GUARANTEED – Buy with confidence! You are assured to get the products as described and get the quick/easy customer service by writing or talking to us directly Smart design:-Made of Anti-slip, BPA free silicone material -Stealth landing: Soft silicone bottom sleeve to prevent your bottle from bumps,dents and dings. -Special design to crate a new looking for your favourite flask SATISFACTION GUARANTEED:-Buy with confidence, 100% satisfaction or 100% money back with our easy/quick after-sale service support by writing or talking to us directly.