World War II cut American designers off from European inspiration and limited the availability of some materials. McCardell flourished under these restrictions. Although many designers considered them too basic, McCardell already worked with fabrics such as denim, calico, and wool jersey that were easily available during the war. She popularized the ballet flat when, responding to the shortage of leather, McCardell commissioned Capezio to produce a range of ballet flats to match her designs. When the government announced a surplus of weather balloon cotton materials in 1944, McCardell quickly bought them up, using them to design clothes that patriotic American women wore with pride.