Recently we have suggested that negative thermal expansion materials will also show an effect called pressure-induced softening, where shown that the elastic stiffness is anomalously reduced on compression. That is, if B is the bulk modulus, the derivative dB/dP is negative. We have previously shown that in Zn(CN)2 that the dB/dP has a striking temperature-dependence, with positive value at low temperature, then quickly falling to a maximal negative value before slowly tending towards zero at high temperature. We have recently predicted from simulation that the same effect in ScF3 may be an order of magnitude larger. The purpose of this proposal is to test this prediction using powder diffraction and performing measurements across the two-dimensional space of both pressure and temperature. The experiment will be performed using the gas cell pressure device within a cryostat.