Yay: Cold water all day. Boo: Lugging around a heavy, insulated vessel. Solution: The stainless-steel Lightweight Trail Series provides some of the best insulation-per-ounce of any water bottle on the market. Weighing less than half a pound and providing 21 ounces of capacity, this double-walled bottle kept our water frosty for 18 hours in 80°F heat while we backpacked near Buffalo National River, Arkansas. (It also keeps liquids hot for about 12 hours.) The soft handle on the cap is easy to grip and durable enough to clip onto your pack, and the bottle held up to months of everyday use both on and off the trail.