The Swatch Skin is 3.9 millimeters thick.
Introduced in 1997, the Skin was created as an exceptionally slim evolution of Swatch’s original plastic watch. Its 3.9 mm case made it one of the thinnest plastic watches in the world and gave the collection its name: the watch was designed to sit lightly and closely against the wearer’s wrist.
The thinness came from Swatch’s effort to simplify the watch’s construction while retaining a quartz movement, plastic case and everyday affordability. Rather than treating slimness as a luxury-watch feature, Swatch used it as part of the brand’s accessible, minimalist design language.
The number refers to the watch’s case thickness, not its diameter, strap width or the thickness of the crystal alone. Later Skin families included variations such as Skin Chrono and Skin .beat, and newer versions have used different case sizes or materials. That is why individual models can have different specifications, but the classic Swatch Skin figure is 3.9 mm.