PLA
Anton means a PEI sheet printbed, which has become quite popular somewhat recently.
@raykholo I have a pei sheet. It’s great.
Heat, no heat?
you might want to give modpodge a try. i roughed up my aluminum bed a bit and smeared a thin layer of the matte (yellow label) stuff on it with a sponge brush.
it can hold on to anything, it’s cheap, and i can still use my inductive sensor as a z-stop.
Does it come off with some sort of solvent just to eliminate any buildup over time?
it comes off easily with a wet rag/towel, and the heatbed set to 45-50C.
So what was supposed to be?
Fight! Fight! Fight!
It is what happens when one printer gets jealous of the printer it is printing parts for. Doesn’t like the thought of competition so it took it out. In this case the part fought back… no clear winner here… 
From what I understand it was a flat piece from the 3Dtje printer on Thingiverse.
Well that explains why the Da Vinci imploded and the PrintRite told me to go f*** myself and ate 2 hot ends when I started using the Printrbot…hmmmmmm. Ugh…bad day. I can hear the Mortal Kombat soundtrack playing in the background now…
This is the part I was printing: http://www.thingiverse.com/download:2524213
@Samer_Najia looks pretty close to what you did.
Your Bad day i must say 
I feel you. It’s hard to find time for me to watch things print in between work and such. If I had a 3d printer business, I’d hire someone to babysit the prints. Give them wages, coffee, and free wifi.
@Kelly_Hale you given any thought to using octopi for remote viewing, least you be able to cancel and switch off if things go pear shape, though imagine it burn like hell too watch the mishap like above unfold live across the web, and damned to do anything about it!!!
The worst part is melting it off of the thermistor wires hoping that it doesn’t break. 