The change in bending rigidity with temperature κðTÞ for 2D materials is highly debated: theoretical works predict both increase and decrease. Here we present measurements of κðTÞ, for a 2D material: AB-stacked bilayer graphene. We obtain κðTÞ from phonon dispersion curves measured with helium atom scattering in the temperature range 320-400 K. We find that the bending rigidity increases with temperature. Assuming a linear dependence over the measured temperature region we obtain κðTÞ ¼ ½ð1.3 AE 0.1Þ þ ð0.006 AE 0.001ÞT=K eV by fitting the data. We discuss this result in the context of existing predictions and room temperature measurements.