That is a tricky one as, while it is not what I meant, it makes sense.
Suggest we have 3 options:
Highest altitude for a Ducati helmet being worn while riding a Ducati which is currently Stelvio Pass @ 9045ft
Highest altitude for a Ducati helmet carried in your hand while walking which is currently Whistlers Mountain, Jasper @ 8,100ft
Highest altitude for a Ducati helmet while in a plane which is an almost unassailable 50,000ft on Concorde - unless someone has taken one into space!!!
What do you know - Martyn is not winning any of them