Noise-canceling headphones regularly top lists of essential travel gadgets, but are they worth it?

A little bit of silence. Sometimes that’s all we want. Whether it’s halfway through a 10-hour flight with a crying baby, or trying to sleep though the snoring from the hotel room next door, the promise of noise-canceling headphones is one that every traveler probably finds intriguing.

Yet are they worth it? These headphones are often expensive and for some people, they don’t live up to the hype.

I’ve spent the majority of the last five years traveling, taking dozens of flights and train journeys, and as someone who has reviewed noise-canceling headphones for even longer, I can definitively say “maybe.

Noise-canceling headphones, also called active noise canceling headphones, use electronic processing to analyze ambient sound and attempt to generate the “opposite” sound. The result is less noise overall.

Imagine ocean waves. There’s high part, the crest and the low part, the trough. If you combined the positive height of the crest and the negative depth of the trough, the result would be a flat sea. Or for the math inclined, if you add +1 and -1 you get 0. This is essentially what active noise-canceling headphones do. Add troughs to crests and crests to troughs. Except instead of seawater, it’s sound waves.

It’s not perfect. these headphones don’t “create” silence, nor are they able to eliminate noise. The crests and troughs do not perfectly cancel out. The absolute best noise-canceling headphones merely reduce noise, and work best with low-frequency droning sounds. So a loud hum is a quieter hum. The roar on an airplane is a quieter roar on an airplane. They also don’t work well for all sounds. At higher frequencies, like the human vocal range and higher, the headphones do very little if anything at all. So if your hope is to block out the cries of the baby in seat 15C, you’re out of luck. Fast and transient sounds, like a door slam or a hand clap, also aren’t blocked effectively.

What’s perhaps even more frustrating is not all noise-canceling headphones work the same. The best reduce a lot of noise, the worst reduce very little or nothing at all. There’s no way to tell, looking at a headphone’s specs, which are which.

Two headphone sets could claim to reduce the same amount of noise but perform completely different. Only hands-on testing, ideally with objective measurements, can tell the difference. Wirecutter, the New York Times Company that reviews products, does these types of measurements for all the noise-canceling headphones they test. (For Wirecutter, I’ve written both the over-ear and in-ear noise-canceling headphone guides along with my colleague Brent Butterworth.)

Noise-canceling headphones require a battery to power their electronics. Noise-isolating headphones, which do not require electronics and therefore can be far cheaper, work by creating a seal in your ear canal to block noise. Basically they are like earplugs, but with earbuds inside. If you can get a good seal, these work reasonably well. Getting a good seal can be a challenge, however, since everyone’s ears are different and not all headphones will fit correctly. And even if you do get a good seal, noise-isolating headphones will not be able to block low-frequency sounds as well as the best noise-canceling headphones. They will reduce a wide range of frequencies, which can help.