Why do Apple's corners look softer?

A bigger radius makes a corner softer.

A standard rounded corner is a straight edge plus a quarter circle, so the bend starts all at once at one point. A continuous corner (often called a squircle) eases into the bend: curvature builds up gradually and is tightest in the middle of the corner. Apple's SwiftUI offers both, as "quarter-circle" and "continuous curvature" corners. In a related study, people who saw objects for 84 ms liked curved versions more than sharp-angled ones (67% against 51%).

The eye picks up the point where a straight edge suddenly becomes a curve; a gradual change in curvature has no such point. This mechanism is a design claim, not a tested finding.

• Use continuous corners where the platform offers them (SwiftUI RoundedRectangle with style .continuous; corner smoothing in Figma, the iOS preset).
• Keep nested corners concentric: inner radius equals outer radius minus the padding.
• Use the same corner style across a product, so cards, buttons and sheets match.

• Claim that continuous corners are proven to be preferred; they have not been tested head to head.
• Fake continuous corners by turning up the radius; a bigger quarter circle still starts abruptly.

• No study found that compares continuous corners with ordinary rounded corners directly.
• Bar and Neta compared curved objects with sharp-angled versions, not two kinds of rounded corner. 14 participants, grayscale images, 84 ms exposure.
• Strong associations (a snake, a chocolate bar) can override the curvature preference.

• JZ-004 · Pretty feels easier