Nature may abhor a vacuum, but I’m a fan of them, especially in water bottles.

I’m always surprised to see how few people bring water with them to the gym in the first place, given how crucial hydration is to performance. Most athletes know that dehydration can reduce their endurance in longer-duration events. But the effect on shorter duration exercise, like sets of weightlifting or CrossFit WODs, is just as impressive: in one study, athletes who were only 2% dehydrated saw their high-intensity exercise performance drop by 45%.

Even fewer people know that the temperature of the water you drink matters, too. Studies have repeatedly shown that drinking colder water helps athletes go longer before reaching exhaustion, at higher mean power output, and improves performance on everything from the bench press to the broad jump.

So, in short, if you’re working out, you should probably be drinking plenty of water, and drinking plenty of cold water, along the way.

That’s where the vacuum comes in. Something like the insulated Kleen Kanteen (my go-to, and The Wirecutter’s top choice) will let you tote 20 ounces of ice cold water to the gym – even if you have to fill it hours and hours in advance (say, filling it with ice water in the morning and then hitting the gym post-work.)

If you’re picking up a Klean Kanteen, I’d suggest you go with the Cafe Cap 2.0 lid. You can sip through it, without needing to unscrew each time you drink, so you’ll drink more frequently. And, as a bonus, you’ll also be less likely to imitate my signature post-workout move: inadvertently pouring the first sip of water from an uncapped bottle down the front of your shirt.