hi Guys,
I just purchased some more PEI to put on other glass pieces I use to have several in rotation. The first time around, both sides of the PEI film were the same - glossy/smooth.
On this last batch, one side is the same glossy/smooth, but the other side is best described as a matt finish. For PEI, does anyone have recommendations on which side should be 'up" for printing?
I had the same question, http://reprap.org/wiki/PEI_build_surface says it doesn’t matter. The smooth side gives you a mirror shiny finish, so I used that, but only if you can get the print off the bed without breaking it 
I prefer the matt side. Sticks better, especially for large parts.
In a technical sense the Matte side is better. Having a matte finish means there is a greater surface area gripping onto the parts in a mechanical fashion. I know Lulzbot ships their bots with Matte side up.
First one is gloss, next will be matt, third, we’ll see what works best! Thanks all!
Yeah, I highly suggest Matte finish. It works loads better imho.
Thanks!