Nope. The leather in 118 and 618 is of the exact same weight and thickness.
All Schott heavyweight leather, that is to say steerhide, cowhide and horsehide - or rather leather 618, 618HH, 613, 118, etc. jackets, if you will - are made of leather which has the same thickness (3 - 3.5oz, if I'm not mistaken).
Schott also offers several jackets made of lightweight cowhide and lambskin, but all these models have stated to have been made of lighter leathers in the name and item description.
To my knowledge, no Perfecto (Brando) model comes in lightweight leather other than the Women's version.
The post from Albatross is correct, but I just want to clarify the labels. We use our "Classic" Perfecto labels in our motorcycle styles. We do have a "Perfecto Brand" label used in limited edition jackets that we produce under this label each season. Gail