On the outside
Whenever I have my off-the-rack shirts altered (usually slimming down the waist) I tell my tailor to do doble pasada which literally means “two passes” or what is commonly known in sewing as a flat-felled seam.
Factories make shirts using industrial sewing machines that gives it seams with two rows of stitching without human intervention. Local tailors don’t have this kind of sewing machines so they must fold the fabric and create two separate rows of stitching that results in a flat-felled seam. On the outside it looks like it was made using the same machines the factories use which is what I wanted to achieve in the first place.
On the inside
So the next time you have shirts or any item of clothing you have altered tell your tailor to do a doble pasada.