The Zip Fly Controversy

Now, let's start with a disclaimer. I'm not that keen on drawing attention to someone else's crotch. This is not a post a draft lightly. But it is an issue that has been bugging me for months. And I think I finally found a perfect illustration thanks to Tilly and the Buttons.

So what's the issue that's got you all fired up, K?

When I started making trousers, I was so sure that every stitching line had to be as close to the centre front seam as possible. The fold of the overlap had to be at centre front, the topstitching had to be at centre front, the centre of the zip had to be at centre front.

So, on various pairs of trousers/jeans you (I) can see topstitching from the underlap, or (heaven forbid) the actual zipper tape.Because it's impossible for all of those things to occupy the centre front at the same time.

Recently I've been worrying if it's only me who has this problem. As if everyone else in the world can have perfect zippers and matching topstitching. And TATB, on their beautiful demo photo, show exactly the problem I have been moaning about to myself. Bless that pink stitching line.

Okay...so...?
If you're in the niche that cares about your you-made clothes looking as good as possible, you will care. That snazzy contrast topstitching won't draw attention where it has no place to be. That surprise coloured zip will remain a surprise. You will finally be able to fix that odd sense of draftiness where your zipper ends. Never again will you worry that it looks like your flies are open even when they're firmly closed.

I had been frustrated because I thought I'd gotten beyond the issue, until B's Quadra's started showing the same symptoms. I followed the instructions on the Quadra fly. I was prepared to come here and spout a load of rubbish about zip-fly conspiracies. I was ready todo a whole series on it. (We could call it The Zip Files...) but instead, I've checked some samples and my sewing books.

The DK Sewing Book - is an authroity on getting you started with a particular technique. Its lapped zip instructions warn that the folded bit of the underlap won't match the seam. It's not so clear on the zip fly instructions, and even assumes that these lines will be marked (has anyone ever seen that?).  In both cases, it's curious that it advises for the overlap to only meet the topstitching - not cover it/go beyond it. I think this is misleading.

David Page Coffin's book Making Trousers for Men & Women has a whole chapter on flies, but doesn't seem to go into this point in detail. Mind you, I find that this book does everything backwards anyway (definitely worth buying+reading if you're interested). But even the front cover sample boasts a massive underlap. No way is the topstitching showing through at the bottom of the zipper.

I checked out some RTW pairs and almost all of them had the underlap at least 1mm behind the seam line. You need to hide the zip, not just cover it up with the overlap.

For jeans in particular, where there was visible topstitching on the crotch seam, the underlap fold was at least as wide as the topstitching there. The line of topstitching on the underlap has the illusion of carrying straight on down on one of the lines of seam topstitching.

The pair below illustrates this very well, but was by far the smallest underlap. Most underlaps were about 1mm - 4mm away from the seam line.

Formal trousers, however - seemed to be much closer to zero underlap. Is this a feature of smaller zips or dress-weight fabric? I have no idea.

So I'm not sure what to say now. I was sure that there would be one "normal" answer and it doesn't look like there is. My top tips for getting a good looking fly are: 1) the fold line of the overlap shoud be at centre front and 2) the underlap should extend underneath the overlap so that everything is hidden.

K