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

Answer: Black absorbs more light

Black absorbs more light ✓ — Correct! Black fabric absorbs more light, reducing its luminance. Lower luminance makes the body's outline appear less distinct, and the brain interprets this as a smaller size. This is a well-known visual illusion called the Helmholtz–Kohlrausch effect, where darker objects are perceived as smaller. Studies show that people wearing black are judged to weigh about 5% less than those wearing white, given the same cut.

Black has higher contrast — Wrong. While black may have higher contrast against a light background, the key factor in the slimming effect is the lower luminance of black itself, not contrast. Contrast can affect visibility but does not directly shrink perceived size; in fact, high contrast often makes shapes appear sharper and larger.

Black has vertical patterns — 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.