If you're not using a foam roller, you should be: Foam-rolling technique is pretty easy to learn, and foam rolling can help improve flexibility and strength, speed up muscle recovery, and maybe even make you better in bed.

But unless you want to use the grimy free-for-all rollers at your local sweatbox, you're probably going to have to invest in your own. So: Which of the approximately 10,348 foam rollers on Amazon should you pick up?

There are three factors to consider when picking out the perfect-for-you foam roller: density, size, and texture, says Paul Mostoff, D.P.T., chief of physical therapy at NYC-based All Sports Physical Therapy.

"The most important characteristic is density," Mostoff says. "A denser foam roller will provide greater compression on muscle knots, which can provide for a better release. However, if you're new to foam rolling or unable to tolerate high amounts of compression, you probably won't be able to apply the compression long enough to achieve a 'muscle release'—so newbies should stick to a less dense roll."

Once you've got density down, you can move on to size and texture. Foam rollers come in a few different sizes, but you're really looking at two categories: longer (at least 3') or shorter (less than 2'). "Larger rollers can be used for rolling out larger muscles like quads, hamstrings, and calf muscles on both sides at the same time, while smaller rollers are better for targeting smaller areas on individual muscle rollers," Mostoff says. (They're also easier to travel with because they're, well, smaller.)

For texture, you've also got (essentially) two categories: smooth and textured. Smooth rollers apply pressure evenly across an area, while textured rollers apply more pressure to specific points in your muscle. This can be good if you want a deeper muscle release, and not so great if you dislike pain. Newbies should stick to smooth rollers and graduate to texture if they want, but veterans shouldn't feel like texture is a necessary step—it's more about preference.