The Pax 2 and 3 have similar sizes, but the difference lies in their efficiency. The Pax 2 takes longer to heat up, requiring about 45 seconds to reach the lowest heat setting. The Pax 3 will reach the lowest heat setting in about 15 seconds, and will only take 20 seconds to achieve the highest setting. Both devices retain the signature Pax appearance. They are both compatible with the replacement screens and the Pax 3 concentrate insert.