A metallic nanoparticle composition includes copper nanoparticles, a first non-aqueous polar protic solvent (boiling point in a range of 180° C. to 250° C. and viscosity in a range of 10 cP to 100 cP at 25° C.), and a second non-aqueous polar protic solvent (boiling point in a range of 280° C. to 300° C. and a viscosity of at least 100 cP at 25° C.). The concentration of copper nanoparticles in the composition is in a range of 32 wt % to 55 wt %, and the concentration of the second non-aqueous polar protic solvent in the composition is in a range of 4 wt % to 10 wt %. There is polyvinylpyrrolidone present on the copper nanoparticles surfaces. The composition's viscosity is at least 250 cP at 25° C.