Not much! Humulin n and novolin n are both forms of nph insulin. Nph Insulin is considered intermediate-acting (generally less than 24 hours in duration, usually 8-12 hours). They are both heavily crystallized solutions of human insulin, which is what gives it the longer-acting property (and cloudy appearance) . Humulin is made by eli lilly & co. (usa), and novolin is made by novo nordisk (denmark).