To investigate the buckling behavior of fibreglass-rotorblades finite-element calculations have been carried out by use of the cured composite-element COMP. The results enable to identify those parameters, which mainly affect buckling, like bending stiffness, curvature, imperfections, fibre orientation. A simplified calculation method is investigated concerning its applicability to fibreglass shells, and is verified by FEM-calculations and results from model-tests. The transformation to other thin fiber-stuructres is presented.