An alternative to the now standardized harness method of securing the gas mask, 'Helmet' or 'skullcap' style gas masks wrap around the head and rely on the tension of the rubber to keep the mask secure. This method was prolific in Soviet Cold-War era gas masks, and can be seen in such masks as the GP-5, the SchMS, the PWRU, the GP-6, and other masks. Other countries [such as Germany, the Netherlands, and Estonia have utilized 'helmet style' gas masks throughout the years, but nowhere near as prevalent as the Soviet Union. Eg. The German WW2 'Volksgasmaske 37' for civilian defense.