A one-component thermosetting epoxy resin composition, including a) at least one epoxy resin A having on average more than one epoxide group per molecule; b) at least one latent hardener for epoxy resins; c) at least one physical or chemical blowing agent BA; d) 3-15 wt.-% of at least one carboxyl group containing acrylonitrile/butadiene rubber ABR1 with a Mooney Viscosity of 15-30 MU (Mooney units), based on the total amount of epoxy resin A; and e) 3-15 wt.-% of at least one carboxyl group containing acrylonitrile/butadiene rubber ABR2 with a Mooney Viscosity of 35-50 MU (Mooney units), based on the total amount of epoxy resin A. The ratio of ABR1 to ABR2 is from 0.5-2.0. The epoxy resin adhesive is notable for the improved storage stability.