SainSmart White Flexible TPU 3D Printing Filament

I bought this in black and yellow, waiting on the multi-color pack to get back in stock now. I spent a week in hell, as I was new to FLEX and had to learn some things the hard way. Punch line: this is AWESOME filament! The yellow looks like a glowing fiber optic when light is nearby, it is simply marvelous!! They are both extremely strong, but also soft and lustrous. Super elastic. You can take the single skirt extrusion and stretch it to perhaps 10 times it's size without breaking, but the material seems to remain slightly stretched if you do that, perhaps 30-60%, but after that it always snaps back to that size. Ordinary prints are super strong and hold their shape perfectly. Here are the bottom line lessons learned if you are new to TPU: LOOSEN THE IDLER!; start at 15-20mm/s for everything except travel; be certain your 1st layer is dialed in well for this filament; and TURN OFF RETRACTION. TPU will wrap itself around your extruder gear, or jam, and speed and retraction are the enemy here. Get it to print, enjoy how amazing it is and be happy, and optimize from there! I have a Prusa i3 MK3. My original hell began on this, and I naively tried to use the stock profile for Sainsmart TPU (I mean, it was there, right?). It seemed to work, but ended up dying mid print, almost always. Ended up wrapped around the extruder gear. Annoying to open things up and unravel it. Rinse and repeat, no joy. Played with very many settings, read very many blogs. Nothing worked. Finally blew the dust off my MK3S upgrade kit, bit the bullet, and spent a bunch of hours tearing down and rebuilding my extruder. Tried again, this time switching to the much more expensive *good filament* I bought (Ninjatek). IT JAMMED AGAIN. WORSE. OVER AND OVER. Finally, it basically tied a knot around the gear and I had to do a 50% disassembly of the extruder to get it out (luckily the MK3S upgrade anticipates this and it's easy). Ditched the Ninjatek (I really dislike that filament, it's expensive, has a dull luster, is too soft, and even harder to print, what a bunch of overhype!). Read a bunch more blogs, and finally realized the only real problem was trying to use the stock profile. The answer was go extreme at first, and optimize after you are happy and can go from there. Here are the full changes I made to the stock Sainsmart profile to start with: - Everybody says "loosen the idler"....but to what?! I had to loosen the idler almost entirely, for me almost the entire screw head was jutting out, and perhaps 1-2 turns of the screw were in the nut. This is super important, and I found you can find the sweet spot by starting loosest (screw just biting), try to load, and tighten until it loads, then stop! Experiment from there. - Bed Temp 70 deg C - Extruder Temp 235 deg C - All print speeds 15mm/s (keeping fast travel speed seemed fine, if a little stringy) - Turned off "keep fan always on" - Enabled auto cooling - Turned off retraction! (in Prusaslic3r this is in the printer settings tab under Extruder 1) I have so far turned the speed up to 35mm/s for infill and it seems to work fine, others say 40mm/s works. I love this filament. After a week of misery, once tuned in it just works every time, good luck!