sorry i should explain

it is part of the order number festo uses
like example :

PUN-H-3-0.5NT

PUN=tubing H=food industry 3.0=outside calibrated in mm 0.5=wall thickness NT=colorless transparent

color codes
BL=blue
GELB=yellow
SW=Black
NT=Transparent

the pun-h series is mostly used to carry Fuel
the PUN-H series are also besto to use for flexible connections like brakes this stuff is less to collapse
the normal pun series are most used for fixed air conectons

hope this is better..