If everything we wear is made of a 2-dimensional fabric, how can our briefs be 3 dimensional.Okay, I got to elaborate this.I am talking in specific of the male upper-undergarment(undershirt),the plain white,cotton garment worn at least by young boys.How is it manufactured without any stitches along

It is because of the tubular/circular knitting.There are machines that knit the fabric into a tube. So,there isnt a need to have a side seam on it. All they have to do is mark the armhole,neckline and shoulder, cut and sew :). your undershirt is made from one such fabric, only.. the width of it would vary! :)

The world famous place for under shirt, (we call them as Banian in India) is Tirupur in Tamil Nadu near Chennai, India. That industry called Hosiery.  Most hosiery garments are made by http://en.wikipedia.org/wiki/Knitting methods. Modern hosiery is usually tight-fitting by virtue of stretchy fabrics and meshes. Older forms include binding to achieve a tight fit. Due to its close fit, most hosiery can be worn as an undergarment, but it is more commonly worn as a combined under/outer garment. There are automated knitting machines. You can Google by typing Tirupur and you get more info.