Is there an easy way to distinguish PLA from ABS by inspection? I've never worked with ABS, but I think I was shipped some by mistake recently when I had to go to another vendor because UltiMachine just can't seem to stock blue PLA. Here is what observed:

It was very difficult to load into the extruder. It took quite a bit of force to force it through the hot end.
It was not feeding well when I tried to print. The hobbed bolt was shaving small pieces from the filament and it was not going through at anywhere near the right rate.
It was firm when it came out of the extruder - not the softness I've gotten used to with PLA.
It smelled different - more like plastic burning than PLA's maple syrup smell.
It extruded much better (although still not as well as I would have liked) when I cranked the extruder up to 235.

If it's ABS, fine. I was going to get to it at some point anyway. But I don't want to be running it at higher temps if it's really PLA.

you probably have the same problem, I have. I cannot get my PLA into the extruder, nor can I figure out what size the extruder nozzle is. This is open source, and pretty much a crap shoot in both information from the so called suppliers as well as forums.. I have had a built prusa mendel for months now and have never been able to even load filament in it Sounds like you have are having better luck than me though

Actually have no problems with PLA - as long as I KNOW it's PLA. Incidentally, I did some digging through piles of receipts and determined it IS ABS that I purchased. I just set it aside for now - I'll get to it later.

What I am amazed at is how, at least for PLA, characteristics can vary color to color. I've been exclusively using Ultimachine PLA, and noticed that with their white PLA, it was almost liquid as it came out of the extruder, and it laid down very unevenly. I also had major problems getting consistent adhesion of the first layer. It would not adhere at all, so I'd lower the head, and then it wouldn't extrude because it was too close to the bed. When I switched to green with the same settings, the experience was MUCH better.\: the extrusion was very smooth and the adhesion issues have been greatly reduced. In retrospect, I should have lowered the temp a bit with the white, but I'm learning. Next time.

You can heat it up and smell its fumes - although not recommended for ABS, it's an easy way to tell them apart.

ABS also tend to "whiten" when flexed, and that whitening can be reverted by heating it.

And last, ABS dissolves pretty well in acetone, bathing a piece of filament for a few hours is enough to see it vanish completely. PLA is damaged by acetone, but not completely dissolved.

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Most of my technical comments should be correct, but is THIS one ?
Anyway, as a rule of thumb, always double check what people write.

That last one looks like the ticket. Like I said, at this point I'm fairly certain it's ABS, but acetone will tell for sure.