How to distinguish between silica gel, acrylic adhesive, pu adhesive protective film

How to distinguish between different glue protective film:
A smell: acrylic adhesive has a foul smell, not silicone, pu glue taste;
2 touch: acrylic adhesive protective film as long as with fingernails will appear a dash of powder, silica gel is not;
See three: acrylic adhesive, pu adhesive protective film cleanliness light transmittance is higher, the silicone protective film is a bit poor.
Four post: stick protective film on the smooth panel, rapid joint is PU glue, silica gel, acrylic adhesive protective film on the slowest.