The 21 oz standard mouth Hydro Flask is ideal for taking on a weekend bike ride or hike to keep your fluids cold. Or take it up the mountain and have hot coffee, cocoa, or soup waiting for you at the end of the day. The Standard Mouth bottle features a larger mouth opening and is ideal for those who need to take in more hydration at a quicker pace. As with all Hydro Flask bottles, they fit perfectly in most car, bicycle, and stroller cup holders and water bottle cages. These water bottles were developed to perform in every environment. Each Hydro Flask is cast from double wall vacuum insulated food grade 18/8 stainless steel, therefore they are BPA-Free and resistant to bacteria and odors. The double wall vacuum insulation technology allows Hydro Flasks to keep contents hot for 12 hours or cold for 24 hours.