Coffee. Naps. Most days when that 2 pm crash starts to creep up on us, those are our two options. If you’re human, you’d love to take the latter. But odds are you settle for the former to give yourself enough of a quick, cheap jolt that you can power through the rest of your day.

You’ve probably also never imagined the two could actually work together. And effectively. “But how?” would be a very logical question for you to ask right now. Coffee is a stimulant. Naps are…well, they’re sleep. The two things could feel or sound more opposite of each other.

Well, a coffee nap is exactly what you probably think it is: drink some coffee and then take a quick 20-minute siesta, with an emphasis on that 20-minute part.

The product is a super-charged version of the power nap. When you drink coffee, it passes your small intestine and is absorbed into your bloodstream. When that reaches your brain, it blocks Adenosine, a chemical compound that is responsible for causing drowsiness by slowing down the activity in your nerve cell. Replacing Adenosine with caffeine in those receptors, as you can imagine, has the exact opposite effect on you, kicking in that hyper-alertness you probably love about caffeine in the first place.

Now let’s mix this with the nap.

While caffeine blocks the receptors normally filled by Adenosine, sleep actually clears Adenosine from them. Conveniently, giving yourself 20 minutes to rest and allow your brain to clear out any Adenosine the natural way is also a perfect amount of time to let your body start metabolizing the coffee you’ve just taken in. In those 20 minutes, you’ve now given caffeine an expressway to start working with the brain without any interference from the drowsy-inducing chemicals that made you want a nap in the first place. Voila, you’ve woken up 10 steps ahead of where you started and it only took 20 minutes, according to science.

Now, napping longer than 20 minutes is going to start having some negative effects on your sleep patterns, as that’s the amount of time your body will start falling into sleep inertia, a physiological state of impaired cognitive and sensory-motor performance you experience immediately after awakening. It persists during the transition of sleep to wakefulness, where you’ll experience feelings of drowsiness, disorientation and a decline in motor dexterity. Basically, wiping away all the positive effects of a coffee nap in the first place.

Researchers insist coffee naps are far more productive than keeping both things mutually exclusive. In the UK, one study found that a 15-minute coffee nap helped subjects score higher on a driving simulator test. Meanwhile, researchers in Japan found that 15-minute coffee nappers scored higher on memory tests than non-coffee nappers. The subjects in that study also reported feeling less tired than the subjects who’d taken the traditional 15-minute power nap without caffeine.