What is the main difference between novolog 70/30 and novolin (insulin)?

Novolog is faster. The '70' portion of both is same, but the '30' portion of NovoLog has faster onset of action <15 min vs about 30 min for novolin (insulin). Otherwise, unit for unit they are about same. The NovoLog thus can be used right before meal, novolin (insulin) should be about 15-30 min before meal. So just timing is different. Consult doc. Good luck.