underwear: what the construction actually means
The word '' gets used loosely in women's underwear marketing. Some styles are genuinely knit in a single tube with no side seams at all. Others just have the seams moved to a less visible place, or have the seam edges bonded flat rather than stitched. The difference matters if you're buying specifically to avoid visible panty lines.
How circular knitting works
True underwear is made on a circular knitting machine, which knits fabric in a continuous tube. The garment is shaped by changing the stitch pattern and tension as the tube is knit, rather than by cutting and sewing separate panels together. The result is a piece with no side seams at all.
The waistband on a genuinely brief is typically a folded edge of the same knit fabric, not a separate piece of elastic sewn on. This is why it sits flat rather than creating a ridge under thin fabric.
What 'bonded seam' means and when it matters
Some underwear marketed as uses conventional cut-and-sew construction but bonds the seam allowances flat with heat rather than stitching them. This reduces bulk compared to a regular seam, but there's still a seam, and the bonded edge can sometimes peel after repeated washing.
For most everyday wear, bonded seams are fine. If you're specifically trying to eliminate any line under very fitted or thin fabric, circular-knit construction is the more reliable option.
Fabric choices in styles
Circular knitting works best with synthetic or synthetic-blend yarns. Most underwear uses a nylon-spandex blend, which has the stretch and recovery needed for the knitting process and holds its shape well over time. Pure cotton doesn't work as well on circular knitting machines because it has less natural stretch.
If you prefer natural fibers, a cotton-modal blend can work in a construction, though the waistband may have slightly more bulk than a pure nylon style. The tradeoff is a softer feel against the skin.
If you're buying underwear specifically for use under fitted pants or dresses, it's worth checking whether the style is circular-knit or just bonded-seam. The product descriptions in the current collection note the construction method for each style.