In this video I’m diving into one of those make-or-break areas on trousers: crotch fit. I’m making the Style Arc Bob Pants, and I’m using FOIL (yes, the actual foil method) to get a really clear read on what’s happening through the crotch curve, inseam, and seat. Instead of guessing and doing tweak-after-tweak in fabric, I’m showing you how I use FOIL to spot drag lines, see where I need more or less length, and make the adjustments in a way that actually feels logical. I talk you through what I’m looking for when I assess the fit, how I decide whether it’s a front or back issue, and how small pattern changes can make a massive difference to comfort and that “smooth” look. If you’ve ever made pants and thought, “Why does this look weird when I sit down?” or “Why is it pulling there?”, this is exactly the kind of fitting session that helps you get to the bottom of it. The big takeaway: FOIL can save you time, fabric, and frustration—especially when you’re trying to nail a personalised crotch fit on a new pattern.