Even within a single type of FDM filament there is an overwhelming amount of choice. Take for example Elegoo’s PETG filament offerings, which include such varieties like ‘Pro’ and ‘Rapid’. Both cost the same, but is there a reason to prefer one over the other, perhaps even just for specific applications? To test this, [Dr. Igor Gaspar] over at the My Tech Fun YouTube channel bought some spools of these two filaments and subjected both to a series of tests.

Obviously, the Rapid filament is rated for higher extrusion speeds – <270 vs <600 mm/s – while the website claims a higher required nozzle temperature that confusingly does not match those listed on the spool. There are quite a few differences in the listed specifications, including the physical and mechanical properties, which make it hard to draw any immediate conclusions. Could you perhaps just use Rapid PETG and forget about the Pro version?

Test objects were printed with a Bambu Lab P1P with an AMS unit. After calibrating the ideal temperature for each filament, a tensile break test gave a win to the Rapid PETG, followed by a layer adhesion test win. This pattern continued across further tests, with Rapid PETG either matching or beating the Pro PETG.

There are only two advantages of the Pro version that can be seen here, which are less moisture sensitivity and  stringing risk, and you of course get the luxury cardboard spool with the closed edges. Whether that’s enough to make you go ‘Pro’ remains to be seen, of course.

We’re probably all familiar with adding wood dust, hemp and carbon fibers to PLA filament, but there are so many other fillers one could add. During the completely unrelated recent heatwave in Germany, [Stefan] from CNCKitchen decided to give a new type of biodegradable filler type a shot by scooping some freshly dried cow patties off the very picturesque grazing fields near his place. In the resulting video a number of questions are answered about this ‘PooLA’ that nobody was asking, such as whether it makes for a good filler, and whether it smells bad while printing.

Perhaps unsurprisingly to those who have spent any amount of time around large herbivores like cows, cow dung doesn’t smell bad since it’s mostly composed of the grass fibers that are left over after the cow’s multiple stomachs and repeated chewing have done their thing. As [Stefan] and his colleagues thus found out was that printing with PooLA smells like printing with grass.

As for the practical benefits of PooLA, it adds a nice coloring, but like other ‘reinforced’ PLA filaments seems to trade flexibility for stiffness, so that at ratios of cow dung powder between 5 to 20% added to the PLA powder the test parts would break faster. Creating the filament was also a bit of a chore, for reasons that [Stefan] still has to figure out.

That said, aside from the technically unneeded bacterial corpses and other detritus in cow patties, using grass fibers in FDM filament isn’t a crazy idea, and might fit right in there with other fibers.