Caps for sealing assemblies for sealing glass containers and maintaining container closure integrity at −80° C. or less are disclosed. The caps include a cap skirt having an annular body and a crimp region. The crimp region is a crimpable metal. The annular body of the cap skirt has a coefficient of thermal expansion (CTE) greater than a CTE of a metal consisting of aluminum, a stiffness greater than or equal to 2 times a stiffness of the crimp region, or both. The greater CTE, stiffness, or both of the cap skirt increase the seal pressure and contact area between the stopper and glass container when cooled to −80° C. or less. The caps enable the sealing assemblies to maintain a helium leakage rate of the sealed glass container of less than or equal to 1.4×10−6 cm3/s at −80° C. or less.