An isogeometric shell element with through-thickness stretch is introduced and applied to quasi-static and dynamic problems. The shell element supports full three-dimensional constitutive laws, ie, the plane stress assumption is not required. An updated Lagrangian rate formulation is adopted, and biquadratic spline-based interpolation functions are used for in-plane interpolation. The concept of fiber mass scaling is proposed to lower the highest eigenfrequencies to improve the performance of the formulation. Clamped and unclamped knot vectors are compared, and the advantages of using unclamped knot vectors are demonstrated. The shell element is validated using several benchmark tests, which indicate good performance of the proposed formulation. KEYWORDS explicit dynamics, isogeometric analysis, large deformations, thick-shell element, unclamped knot vectors Recently, the focus in the shell finite element technology has shifted toward more advanced formulations, such as thickness stretchable shell elements and solid shells. Two isogeometric solid-shell elements have been proposed by Hosseini et al 20,21 ; the latter formulation was extended to model propagation of delamination in composite materials. 22 Int J Numer Methods Eng. 2019;119:105-127.wileyonlinelibrary.com/journal/nme