If we are referring to piston that is used in Hull (Pro piston), Cheddite (Free Shots), Fiocchi (F3 Bior):
...piston wad sports a "skirt" (under) and a "cup" (over).
- Skirt
should seal the gasses in backbored barrels better than fibre
- Cup holds some shot that
should serve as a wedge that
should spread shot more than fibre wad...in theory
Then there is piston wad that is found in Fiocchi (F3 Piston), and Clever (T4 Pro sporting) and is called by Gualandi a "Skeet piston wad" :
- Skirt is quite shorter than on previous one - tho
should still seal gasses better than fibre wad...
- Cup is longer than on previous one - still shorter than in trap shells -
should fit between regular and bior/short piston/fibre wad - Clever goes even further stating that this wad gives best results between 30 and 45 meters...in theory
While I may be buying the sealing part the rest is debatable - but sells rather well I believe - all fun and games.
Iggy - Cheddite smart strike has Aquila (regular) wad that is used in their Sporting, Universal trap, 3 mach (regular) cartridges: