A filament strand (40) for additive printing includes a first core (63) comprising glass fiber (62), the first core (63) comprising between about 10%-50% by weight of the filament strand (40), a second core (65) comprising carbon fiber (64), the second core (65) comprising between about 5%-30% by weight of the filament strand (40), a thermoplastic matrix (60) comprising between about 50%-80% by weight of the filament strand (40), and a thermoplastic sizing (66, 67) coating at least one of the first (63) and second (65) cores.