When it comes to a thin strap bra, the key to good support is finding one that fits properly. If the band is too loose, there will be gaps where the breasts aren’t held in place (strapless bras exist for a reason). The back should form a straight line around your torso and not ride up higher than the front. If you’re wearing a bra that does this, try going down a band size and up a cup size to solve the problem.

The straps are responsible for no more than 10% of the actual support of a bra (this is why we have strap pads, after all). If they’re digging in and giving you those “armpit bumps” that many women complain about, it means your band needs to be tighter. You also may need to go down a cup size if the bridge (also called a gore) is sitting too high, which will push the wire of the cup into your rib cage and create a double-boob look.

Another sign that your bra is too big is when the back is pulling up and it’s no longer a straight line around your torso, or if the band digs in and is too snug against your skin. To check your band fit, take a measuring tape and wrap it across the back of your chest where your bra sits. You should be able to comfortably fit a finger beneath the tape measure. If the measurement is an odd number, round it up to the nearest whole number. Then subtract your band size from the cup size to find your bust size.

If you’re experiencing red marks on your shoulders from your straps, that isn’t normal and it could be a sign that you need to go down a size in both the band and the cups. The fabric used in most straps isn’t designed to press against your skin and can cause these marks. If the marks are causing bruising or lasting more than an hour, it’s time to double-check your fit and get a new bra. The best bras for thin straps will have brushed elastic at the rib cage that’s comfortable and soft on your skin. They’ll also be lightweight and breathable, which will keep you cool during workouts. This sports bra is a perfect example with its light, quick-drying material and simple silhouette that’s both flattering and functional. The straps are a little more narrow, too, which makes this bra great for thin or small-framed women. You can even wear it under a shirt.