Why do some planes leave long trails, but others don't?

[link to contrailscience.com]

Good question. I know what I think; however, I will let Menow answer this one.

I now see your website reference. Good info. However, this is not the answer to several questions that haunt people who believe there are Chemtrails.

Sorry, I said I wouldn't post anymore on Chemtrails so I need the OP or someone to allow me to go on further.