Evidence of how temperature plays a role in the magnetic irreversibility in the intermediate state of a cylinder and various disks of pure type-I superconducting lead is presented. Isothermal measurements of first magnetization curves and hysteresis cycles are analyzed in a reduced representation that defines an equilibrium state for flux penetration in all the samples and reveals that flux expulsion depends on temperature in the disks but not in the cylinder. The magnetic field at which irreversibility sets in along the descending branch of the cycle and the remnant magnetization at zero field are found to decrease with temperature. The contributions to irreversibility of the geometrical barrier and the energy minima associated with stress defects that act as pinning centers on normal-superconductor interfaces are discussed in an effort to account for the results obtained.