The drafting rules, and where they come from
Sloper Studio is not a pattern store and not an image generator. It is a parametric drafting engine: your measurements go in, and documented pattern-making rules compute every line, curve, and dart of your pattern. This page explains exactly how that works, and what we do and don't claim.
Our drafting formulas are based on Metric Pattern Cutting for Women's Wear by Winifred Aldrich, one of the most widely used flat pattern drafting systems in fashion education. Where Aldrich's methods have documented limitations (they do), we cross-reference commercial pattern standards, indie pattern company practices, and peer-reviewed comparative studies of drafting systems.
Every number in the engine traces to a source. Dart intake distribution, armhole depth, crotch curve extensions, sleeve cap height, ease allowances: none of it is guessed, and none of it is generated by a language model. If we change a formula, it's because testing or published research told us to.
Commercial patterns are drafted once at a base size and scaled up and down. That's why they fit the fit model and almost nobody else. Sloper Studio computes the geometry fresh from your measurements every time: your bust-to-waist ratio, your height, your rise. There is no “size 12” underneath.
The engine works in millimeters end to end, and exports at true 1:1 scale. What you print is exactly what the math produced, with a calibration square so you can verify your printer didn't distort it.
The same body needs a different pattern in denim than in jersey. The engine adjusts ease, dart intake, and seam allowances by fabric type: full ease and darts for wovens, reduced for stretch wovens, and negative ease with suppressed darts for knits. Seam allowances are set per edge, narrower on curves like necklines and armholes and wider on hems, following industry conventions rather than a single uniform allowance.
AI helps interpret what you want (for example, turning a text description into design settings). It does not draw your pattern. The geometry always comes from the parametric engine and its documented formulas. We describe Sloper Studio as AI-assisted parametric patterns, not AI-generated patterns. The distinction matters, and the sewing community is right to be skeptical of the latter.
Formulas are necessary but not sufficient. Real bodies vary in ways measurement charts don't capture. Our testing protocol has three phases: internal sewing tests of every garment, external testing with recruited testers across the full size range (multiple testers per measurement band, standardized fit feedback, photo documentation), and iteration on the formulas based on what testers find.
Honest status: we are currently in the testing phase. No garment gets a “tested” badge until it has been sewn and evaluated on real bodies across sizes, and we will publish the testing results, including what we had to fix.
Want to be part of that? Apply to become a pattern tester. Testers receive free custom-fitted patterns and compensation for completed feedback.
Aldrich's system was developed from UK sizing surveys and assumes proportions scale linearly, an assumption that breaks down for some body types, particularly at the ends of the size range. We're building measurement-band corrections (petite adjustments, plus-size proportional adjustments, shoulder slope overrides) informed by newer body-shape research, and external testing across the full size range is how we find what still needs fixing. If a pattern doesn't work for your body, that's a bug. We want to hear about it.
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