Skim through

What it does: binding, film forming, hair fixing 

The science

VP/VA Copolymer is a big polymer (created from repeating subunits) molecule that works as a film former and hair fixative agent. It is a modified version of the first and classic hair fixative, PVP, that alternates the water-loving VP (Vinyl Pyrrolidone) units with water-hating VA (Vinyl Acetate) units to create a film that is less brittle and less sensitive to air humidity. 

Benefits for your hair

Promotes styling ability

VP/VA copolymer helps hair hold its style by inhibiting the hair's ability to absorb moisture. VP/VA copolymer dries to form a thin coating, which prevents moisture entering.

TLDR 

VP/VA copolymer is a great ingredient for helping hair to hold its style by forming a thin layer which prevents moisture from being absorbed.