Chemtrails- What are they made of?

I have been seeing these since 1997 when I was in Columbus, Ohio.  I soon realized as I traveled across the USA that these chemical trails were a nationwide  phenomenon.  Although I am not certain as to the reason they present, they do appear to be different than condensation trails- which disappear after a few seconds. Chem trails frequently turn a crystal blue sky into a hazy sky as clouds are seeded from the substance sprayed into the atmosphere.