Center Back Seam Bikini Bottom

The Original Brazilian Style ...

The centre back seam is a modification made to an existing bottom pattern. You can apply it to either the band or string side bikini bottom. Indeed you can even apply it to some one-piece patterns. The objective of having a centre back seam is to lock the garment in place and stop it riding up ... and give the appearance of a better fit. It seems counter-intuitive considering, by definition, it is set between the cheeks. What actually happens is by locking between the cheeks the garment can use the cheeks to locate each bottom panel in sort of the same way a fishing net stays open when pulled through the water. This is a very stable bottom design. The visual difference is the garment sits between the crests of the cheeks rather than out over them. As such it’s a design much more suited to the younger figure.


The centre back seam used to be the single defining feature of high fashion swimwear as more and more of the expensive labels move toward an even closer fit … I first did this in 2001! ... unfortunately more frequently nowadays we're seeing ill fitting full width swimwear being bunched up between the cheeks


The first photo below is the pattern we are going to create. It's a modification, or perhaps the next step, of the band side bikini bottom. Firstly take a look at the size chart and notice the difference in the two gusset measurements. The centre back seam sits in a similar position to the thong so we need to remove at least 4.5cm of length for a size 10. Because the design itself is so close fitting it tends to look too long in the seat for such a narrow back, so we snip out a further 1.5cm (really just lowering the final waist line of the garment. We achieve all this by taking half out of the crotch area and half out in the darts we use to create the curved centre back seam.

The first photo is one of mine from 2004, photo by Chris Huzzard. Remaining two photos found on the Internet (I do not own copyright); used for the purpose of illustration/education only.

This pattern is based on the size 10 band side pattern we created previously. Before you start each step, take a good look at the illustration to help you follow the drafting process. At the end of each step your draft should match the illustration.

Step One

Remove any seam allowance from the pattern. Draft a horizontal line 3cm above the current crotch seam and remove the area from the pattern.

Step Two

Bring the front and back panels back together being sure to line up the centre line. Redraft the leg line completely concave. You are removing the section that would normally extend out over the cheeks. Keep in mind that no matter how narrow it looks on the pattern, it will look even narrower on the body. This pattern will result in a Brazilian width seat. If you wanted a wider seat you'd need to take a bit of side band from the front and add it to the back panel first. Notice that I've also narrowed the width of the side band in keeping with the style of the garment.

Step Three

Draft in two guide lines, one half way along the centre back and the other half way between the first and the crotch seam.

Step Four

Trace the back panel and close out each dart by 1.5cm as illustrated in red.

Step Five

Recurve the centre back seam and leg line smoothly.

Step Six

Remove unnecessary guidelines. If necessary retrace the front and back panels. Add seam allowance to the pattern based on how you intend to assemble it. I've shown this pattern with 10mm allowance for overlocked seams (8mm to blade plus 2mm off cut) and 10mm allowance for folding over 9mm elastic. If you were to use a binder attachment to apply the elastic and casing fabric to the edge, then you wouldn’t need any seam allowance on those particular seams. Finally, be sure to clearly label your pattern pieces with a title, panel name, garment size, cutting instructions, author’s name, date and revision number.

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