Sealing spring fastener with hermetically closed cavity

A sealing spring fastener comprising:

• a U-shaped structure having a first side, a second side, a top end, a bottom end, an upper section, and a lower section;
• a spring leg on each side of the U-shaped structure, extending outwardly from said U-shaped structure in a general direction from the bottom end toward the top end, each spring leg having an attached end and a free end;
• a casing surrounding at least partially the lower section of the U-shaped structure, except at least the free end of each extending leg, the casing enclosing a cavity within the first side and the second side of said U-shaped structure, the casing having an upper sector and a lower sector;
• and
• an elastic body comprised of at least a gasket, the gasket extending away from the closed cavity in the vicinity of the top of the U-shaped structure, the gasket having an upper side and a lower side;
• wherein the casing has lower ultimate elongation, higher Shore hardness, and higher shear strength than the elastic body.