Negative regulator of the heat shock response. Negatively affects HSF1 DNA-binding activity. May have a role in the suppression of the activation of the stress response during the aging process (By similarity). Homohexamer. Associates with heptad repeats of HSF1 trimers and probably also HSF1 monomers, and with HSP70. Association with HSF1 trimers and HSP70 coincides with attenuation of heat shock response and the conversion of HSF1 trimer to monomer (By similarity). Belongs to the HSBP1 family.