Vandoren V12 reeds have a longer palette, which means that more of the reed is vibrating, resulting in a deeper, richer sound. Bb clarinet V-12 reeds are manufactured from cane tubes with the same diameter as cane used for alto saxophone reeds. As a result, they have a thicker heel and are cut on a longer palette with a slightly thicker tip than the Traditionals. The longer palette means that more of the reed is vibrating, resulting in a deeper, richer sound. The thicker tip gives body to the attackand also increases the longevity of the reed. -the manufacturer
The 3.5+ is a special "in-between" strength for the Vandoren V-12 Clarinet reed for those that want a reed just a little stiffer than the CR1935.