Hydro Flask's Standard Mouth Loop Cap is designed for everyday use as well as challenging outdoor environments. It provides a leak proof seal which aides in keeping your Hydro Flask contents cold or hot. Clip to a backpack or messenger bag and take your bottle on the road. For Hydroflask standard mouth Bottles (Campmor sku# 80302 and 80303.) Also fits other standard mouth bottles with 1.875" opening. Made from polypropylene, which means they are BPA-Free.