✅ Functional--It was specially designed for Stanley Quencher Adventure 40oz 30oz Tumbler & IceFlow 20oz 30oz. It is also compatible with Hydro flask Wide Mouth(12/16/18/20/24 oz), Hydro Standard Mouth(18/21/24 oz), Hydrojug Traveler 32oz 40oz tumbler, Owala flask Freesip & Flip 24oz. Yeti Rambler Tumbler/Travel Mug(20/30oz),Vmini Wide Mouth Flask 12/24oz, Vmini Standard Mouth Flask(12/18/22 oz) and others flask which bottom diameter is 2.83-2.95inch ✅ Smart idea--Heyskay offers more designs to choose, it is easier to find your style to pretty up your expensive flask water bottle. And it will protect your flask from scratch and dings, also no noise any more when landing your flask on desk ✅ Safe material--Heyskay silicone boots are made of high quality food grade soft silicone material, BPA free, odor-free, feel safe for your daily use ✅ Portable to carry--Reusable, washable and foldable. Our silicone 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 wiring or talking to us directly. About HEYSKAY flask silicone boot-BPA free soft silicone material-Fits Hydro flask perfectly and the other brands which diameter is the same as Hydro flask like as Simple, Mira, Yeti (note: a bit tight for Yeti but ok to put on) Bright up your Hydro flask look-No noise any more when landing your flask on desk and protect your flask bottom from damage, smart idea!