Seamless briefs and how they are made

Short answer: Seamless briefs are knitted in one piece on a circular knitting machine instead of being sewn together from several parts. That is why there are no side seams to show or rub.

Knitted in one piece

The machine knits the whole pair round like a tube, with no parts to sew together afterwards. That is the big difference from ordinary briefs, where front, back and sides are cut separately and sewn together. Only the gusset and sometimes the edges are added once the briefs are knitted. See bamboo briefs.

How the machine works

A circular knitting machine has its needles arranged in a ring and knits the fabric round and round. It can switch between different stitches along the way, so the fabric is denser in one place and stretchier in another. That way the waistband, legs and crotch each get their own properties, even though the briefs are one piece.

The gusset comes afterwards

Even though the rest of the briefs is knitted in one piece, the gusset is usually sewn in afterwards. It is an extra layer on the inside that deals with moisture. The seams there lie low and flat, in a spot where they do not show through clothes, so the briefs still look seamless from outside.

Why they do not show

Without side seams there is no thickening in the fabric, and so no line under fitted clothes. Where sewn briefs have a seam on each side and often elastic at the edge, the seamless transition simply blends into the fabric. That makes them an obvious choice under leggings. See bamboo underwear for women.

No seam to rub

A seam is not just something you see. You can feel it too, especially when you move a lot, sit for long periods or wear fitted clothes. Without side seams there are fewer places where fabric can rub against the skin. Many people find seamless briefs calmer to wear for a whole day.

The fit is different

Because there are no seams, the briefs follow the body more directly. The fabric gives in every direction and shapes itself to you. That means the size is more noticeable than in a sewn style. If they are too tight you feel it everywhere, and if they are too big they can fold.

Choose the size with care

Measure around your hips and compare with the size chart rather than going by the size you usually wear. If you are between two sizes, think about how you want them to sit. The smaller one sits closer and smoother, while the larger one gives a little more room around the waist.

Wash gently

Circular knitted fabrics stretch more easily when wet. Avoid wringing them, and press the water out gently with a towel instead. Wash at 40 degrees with a mild detergent and skip the fabric softener, so the gusset keeps its ability to move moisture. See washing and care.

Dry on low heat

Dry them on low heat or hang them up. High heat can make the knit contract and change the fit. Lay them flat or hang them over a rail, so they are not pulled out of shape by their own weight. That way they keep their shape for longer.