The whole entire sock is elastic with an elastic Velcro strap. Sizes XS-S/M- L and XL Up to six times more durable than Finnmark sock Width (flat dimensions)Circumference XS: 65-100 mm / 130-200 mm / 140 mm S: 70-110 mm /150-220 mm / 140 mm M: 80-110 mm / 160-230 mm / 140 mm L: 85-120 mm /170-240 mm / 150 mm XL 95-135 mm /190-270 mm / 160 mm