The terms earbuds and earphones might seem interchangeable, but they usually indicate an important distinction. For our purposes, earbuds don't enter your ear canal but sit just outside. This design fits more loosely and can cause problems with accurate stereo imaging (in which both ears get the same amount of audio) and bass response.

In-ear earphones, meanwhile, have silicone or foam tips that fit in the ear canal and form a seal inside your ear, blocking outside noise while piping sound directly into your ears. These often come with eartips in different sizes that help ensure the best possible seal. Others ship with additional flexible fins that provide even more fit security.

The term earbuds has become synonymous with earphones and in-ear headphones, so the difference is ultimately academic. Whatever you call them and whatever they say on the box, you should look for earphones with tips that form a good seal inside your ear. They sound much better than models with plastic-covered drivers that rest loosely against your ear canal.

Battery life is a weakness in the wireless category. The best pairs can last up to 10 hours on a full charge, though the worst last only a few hours. This is why charging cases with internal batteries are critical to the equation.

That said, I don't see many runners carrying a charging case and docking earpieces for extra battery life on their long runs. But this is also because—again, ultra-marathoners, this excludes you—most of these battery life ratings are sufficient for runs. If you run a full marathon, your wireless in-ears can likely last most of, if not the entire race. If you run a half marathon, you almost certainly don't need to worry about running out of juice. Of course, the battery life depends heavily on volume levels, so one way to get a longer result is by listening at lower levels.

If you're going to wear wireless earphones for running or other types of exercise, some level of water resistance is vital. You can check how protected your earbuds are against the elements by looking at their IP rating, the standard that describes how well a device handles dust and water.

The last number in an IP rating indicates a device's water resistance; earphones with an IPX7 or IPX8 rating are safe even if you submerge them completely in water, for example. For handling sweat, a rating of at least IPX5 is generally sufficient. Earphones with an IPX4 rating can handle moisture, but you shouldn't rinse them off under a faucet.

The first number in an IP rating refers to dust resistance, but sometimes manufacturers don't officially certify products against dust. If a product has an IP rating that starts with IPX and then a number (e.g., IPX6), the device is technically rated only against water.

Most runners—except for, perhaps, ultra-marathoners doing desert runs—don't need to worry too much about dust protection ratings, but water and sweat resistance are crucial. Beware of manufacturers that claim a product is "waterproof" even if it has a low IP rating and can't withstand substantial water pressure.