Why does a black outfit sometimes make a person look slimmer than a white one, even when the clothing cut is identical?

Answer: Black fabric reflects less light, so its edges look sharper

Black fabric reflects less light, so its edges look sharper ✓ — Correct! Black fabric reflects much less light, so highlights, shadows, wrinkles and edge cues are less visible. With fewer bright contours, the body's outline can look less expanded than the same cut in white. A related effect is the irradiation illusion: bright areas appear to spread slightly beyond their true edges, dark areas do not. So black does not literally shrink the body; it reduces the visual cues that make a silhouette look broader.

Black fabric has built-in vertical patterns that elongate the figure — Wrong. Vertical patterns can create a lengthening illusion, but the question specifies the same cut—no added patterns. The slimming effect of black is purely due to its light-absorbing property, not any pattern. Without vertical stripes, the dark color alone still works by reducing luminance.

Black fabric creates stronger contrast with the background, so the body looks narrower — Wrong. Background contrast can make a silhouette easier or harder to notice, but it is not the main reason black clothing reads as slimming. The more direct cue is that black fabric gives the eye fewer bright surface details and less apparent edge spread than white fabric.