Jet contrails, which occur at high altitudes (e.g., 40,000 feet) disappear quickly – much like your breath on a cold winter day.  They are simply made of water vapor.

Clouds need 70% moisture to form.  Contrails need low humidity (moisture) to form. 

As top-notch researcher Clifford Carnicom notes, “If ‘contrails’ by appearance transform into ‘clouds’, it can be concluded that the material of composition is not water vapor.”

What this means:  If what looks like a contrail then becomes a cloud, it isn’t made of water vapor.