Vandoren V12 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 pallet with a slightly thicker tip than the Traditional. The longer pallet means that more of the reed is vibrating. The thicker tip gives body to the attack and also increases the longevity of the reed.
Comparing strengths, a V12 strength 4 reed is almost equal to Traditional strength 3 1/2 reed.