A thin strap bra lets you show off a little skin while keeping your bust in place. These styles come in a variety of colors and materials, but the best thin strap bras can do more than just look good under your clothes—they can also support you all day long.

If you’re wearing the right size bra, the wide straps should feel comfortable and dig into your skin rather than cutting into it. If you’re experiencing deep red marks, however, that could mean that your band is the wrong size or it has stretched over time. The majority of lift in a bra comes from the band, not the cups, so the band should fit snugly and not be able to pull away from your body.

The best thin strap bras have a band that can keep the cups close to your skin and shouldn’t be too tight or loose. To figure out your band size, wrap a tape measure around your underbust (taking a few deep breaths to ensure it’s not too tight) and add four inches. That will give you your band size, and subtracting your bust measurement from that will tell you what cup size you need.

If you’re noticing gaps or spillage, the cup size is probably too small, according to the bra-fitting brain trust at the Reddit board A Bra That Fits. Likewise, if the cups are too large and creating a cradle effect, you’ll need to go down a cup size. You may also want to try securing the band on a different hook to see if you can get a better fit.