The differnce is that Contrails ( from jet engines ) evaporate quickly behind the plane, just like your breath evaporates quickly after you breathe out on a cold morning. Chemtrails persist in the sky for a long time, and spread out across the sky, creating a sort of soup-like fog type of cloud. Sometimes you can observe the planes turning the sprays on and off again. You cannot do that with Contrails, but you can do it with sprays. It's full of Aluminium in an aerosol form, toxic to all life. The idea is that it reflects sunlight back into space, thus cooling the earth, But the problem is, it also creates a "blanket" that traps the heat in too. It's just an excuse they use for carrying out their goal of "managing" the weather for their goal of carrying out Agenda 21.