Quick answer

Choose a thong or low-rise style with bonded or ultra-thin edges and a smooth, stretch fabric, then size it so it lies flat without digging. For most leggings, a seamless thong under leggings works better than a full-coverage brief because it removes the back-panel edge that creates the line.

Why leggings make every edge visible

Leggings are usually a thin, stretch knit that conforms to the body. Any ridge underneath, such as a waistband, a leg opening, or a folded seam, presses into that knit and shows as a line or a shadow. The fix is not always a different legging. It is reducing the number of edges and the thickness of those edges under the fabric.

Match the underwear edge to the legging weight

Thin, high-stretch leggings reveal more, so they need underwear with the flattest possible edge. A bonded edge, laser-cut edge, or a very fine mesh lies closer to the skin than a traditional stitched elastic. If your leggings are a thicker ponte or a compression fabric, you have more room to wear a cotton bralette-style brief or a standard thong without a visible line.

Fit is the line you cannot see

Underwear that is too small digs in and creates a ridge. Underwear that is too large folds and bunches. Both show under leggings. Check that the waistband sits flat when you move, and that the leg openings do not roll. If you are between sizes, size up in a stretch microfiber and size down only in a firm, low-stretch mesh.

Diagnose your visible panty line

  • Line across the back of the thigh: This is usually the back edge of a brief or a high-leg cut. Switch to a thong or a high-cut style with a bonded or raw edge so there is no folded fabric under the legging. If the line disappears when you switch to a thong, the cause was the back panel edge.
  • Ridge around the waist or hip: A waistband that is too tight or too wide for the legging rise shows as a horizontal band. Choose a low-rise style that sits below the legging waistband, or a seamless waistband that lies flat. If the ridge remains, the waistband is too small. Size up before changing styles.
  • Bunching or a lumpy shadow: Fabric that folds under the legging is often a size issue, not a style issue. Try a stretch microfiber in your usual size or one size up, and check that the gusset lies flat. If bunching continues, the underwear is too large for the legging tension. Try a firmer, thinner mesh.

Products that solve the line problem

  • Heavenly Stretch Thong - Champagne: Buttery soft, 4-way stretch microfiber with a liquid hand feel and completely bonded edging, plus a 100% cotton jersey gusset liner. The bonded edging removes the bulky stitched seam that usually causes a visible line, and the 4-way stretch moves with leggings instead of pressing into them.
  • Gossamer Mesh Hip G Thong Underwear - Pink Dream: Superfine Italian mesh with a signature delicate edge and a low-rise fit, and it air dries in under 8 minutes. The ultra-light mesh and low-rise cut sit flat under thin leggings, and the fast dry time makes it practical for daily wear or travel.