No. They're not. But conspiracy theorists love them anyway.

So which is the plausible explanation?

1. That the government is somehow either fitting chemical dosing equipment to commercial airliners, or doctoring the fuel supplied by multinational fuel companies, and managing to cover the whole thing up. And whatever they're dosing us with, it survives the extreme temperatures inside a jet engine.

or

2. When you burn any hydrocarbon fuel in oxygen, you put hydrogen, carbon and oxygen in, and get water (hydrogen and oxygen) CO2 (carbon and oxygen) and energy as a result. If you burn hydrogen alone (no carbon) you just get the water and the energy. And those visible vapour trails are that water.

Complete bullshit.

Of course nobody has irrefutable proof, they don't need it. There are literally thousands of videos on YouTube with people screaming "wake up sheeple" over pictures of aeroplanes... why on earth would you want more proof than that?

It's bunk. Loads and loads of bunk

Tin foil hat BS.

surely they are effluent from spent benzine ?

Totally conspiracy BS.

I call BS. though many of my friends argue with me over it.

chemtrails always appear in the weirdest conversations....it is way low in my probability scale for one simple fact: who is poisoning their own air (intentionally, not just polluting it)? The moment you see the wealthy wearing Self Contained Urban Body Suits, or S.C.U.B.S. (I'm trademarking this so I can be one of those wealthy bastards) telling us it is a fashion statement and not to worry, then we can have that discussion over again....hehe

Chemtrails are contrails of water vapor and not part of any conspiracy. The tin hat crowd keeps working overtime on this one whilst missing out on the real conspiracy stuff.