How thick is the skin of an aircraft like the Airbus A350 or Boeing B777?
From whats written here 


  f100 skin is 1.0 - 1.4mm  
  
  b747 skin is 1.8 - 2.2mm  
  
  a320 skin is about 1.1mm


According this article on the 757


  ...Although Boeing specified that the skin in that area of the
  fuselage must be 0.039in (0.99mm) thick...


Some interesting info here as well.