Mylar is good for a main sail and Dacron is good for a jib.

Mylar will hold it's shape longer but is more suseptable to damage from ragging the sail or improper rolling of the sail. Once you put a crease in Mylar it is there to stay so you can never fold a Mylar sail.

Dacron is a great material for Jibs because it withstands abuse very well. Dacron is also a pretty good material for mains but because it stretches easier than Mylar most racing sailors like Mylar better.

And I forgot to say welcome to the forum and to catamaran sailing.

Keep One Hull Flying,
Mike Hill
H20 #791