I've been trying out a 1mm thick sheet of PEI for the past week on my X1 and all i can say is WHY NAVEN'T I TRIED THIS! I exclusively print with ABS and thought i had a pretty good process with an aluminum bed (for flatness and even heating) with Bed Weld. But wow i just stick this PEI on with some binder clips and WOW it's almost like cheating. The adhesion is perfect with ABS, first layer is sticks great, but easy to peel off with just a bit of cooling time (you can just remover the sheet and flex things off if you're impatient like me). The bottom layer of my prints is a a great mirror finish. The only thing that's slightly annoying is i need to use 8 binder clips to keep it from warping on long/big prints (3 on each end and 1 on each side) but OMG is it worth it. I'm going to order a 1.5mm or 2mm sheet soon so that shouldn't be an issue anymore... Just thought i'd spread the good news bc i've def lost days out of my life due to first layer problems. Here is the Amazon link, happy printing!

https://www.amazon.com/gp/product/B074XG1NDM/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1