Flat seams and what they mean for the skin

Short answer: A flatlock seam lies flat with no ridge on the inside. That is the detail that decides whether underwear chafes on a long day.

What a flatlock is

Two pieces of fabric are sewn edge to edge rather than overlapping. The result is a seam as thick as the rest of the fabric with no ridge against the skin. You can recognise it by two parallel rows of stitching.

Where it matters most

In underwear, sportswear and anything worn close for many hours. An ordinary seam with a ridge can leave a groove in the skin after eight hours. A flatlock does not. See bamboo underwear for men.

How to check

Turn the garment over and run a finger along the seam. If you can feel a ridge, it is not a flatlock. If you can barely feel where the seam is, it is. See bamboo underwear for women and bamboo activewear for women.

Frequently asked questions

Is flatlock stronger

Not necessarily stronger, but flatter and more comfortable against the skin.

Is there underwear with no seams at all

Yes, seamless styles where the edges are bonded or knitted in. They are flatter still.

Is it stated in the description

Often. Look for the words flat seam, flatlock or seamless.