The Hydro Flask 21oz Standard Flex Cap is a reusable, refillable water bottle made of stainless steel. It's compatible with most cup holders and features TempShield double-wall vacuum insulation, which keeps cold drinks cold for 24 hours and hot drinks hot for up to 12 hours. The bottle is leakproof when closed, BPA-free, and dishwasher safe. It's also durable and fits most cup holders. The Surf color is a great option for those who want a stylish and functional water bottle. This unisex water bottle is perfect for anyone who wants to stay hydrated on-the-go.