The Klean Kanteen Wide Loop Cap surpasses all plastic and paper alternatives. With its large, 54mm opening, liquid can easily be filled inside the 100% stainless steel interior.
Even though it's wider, it's still easy to clean, as it has smooth, rounded corners. The backcountry water filter is also compatible with it. Additionally, it won't alter the flavours of the things that are kept inside it.
It comes with a lifetime warranty as well, and it's dishwasher safe because it's made from durable materials.