The Luftkappe from Vorsprung Suspension increases negative air volume in air spring forks.  This greatly improves the two main issues with air springs: a high starting preload and a weak mid-stroke.  The extra negative volume lowers starting preload to zero, creating a pneumatic top-out effect.  The reduced initial spring rate allows higher air pressure for better mid stroke support along with improved small bump sensitivity.

The Luftkappe NA1 kit also includes a low volume seal-head to upgrade the negative air volume similar to Fox 2018 Evol spec.

Compatibility:
Fox 36 NA 2015-2017:
NA air system only.  Does not work with TALAS or FLOAT air spring systems.
Use EVOL version for 2018+ forks, luftkappe is the same but seal head isn't required in those.
Max 3 tokens due to reduced internal clearance.  Suggest tuning starts with 1 token.
SD Components DVC compatability is yet to be determined.
MRP Ramp Control compatability is yet to be determined