The stuff I use has particles which are about 2cm across, I use it because of Brian Barnett's recommendation. Having said that, I've seen some of the world's best breeders' incubators with eggs incubating in the fine stuff!
I haven't found anyone who says that fine stuff is better, and from first hand experience I can't recall anyone other than Brian recommending co**** stuff, but no one says co**** is worse, so that's what I use. It's cheapest from hydroponics stores. Be careful, I've gone to a few places, asked for co**** vermiculite, been handed a large opaque bag, and told it's what I want. I've said I want to see it before I buy it, the assure me it's co****, I say that I'll pay once I see it, they say it'll destroy the bag, etc etc, I tell them if it's what they say it is it will be my bag, and they'll only be destroying their own bag if what they're saying is untrue, so they cut them open... I've seen a few red-faced hydroponics store owners that way
The laugh is almost worth the wasted time and fuel
