Almost all of the filament suppliers vacuum seal their filament with a desiccant packet pack to ensure your filament arrives dry and ready to use. That’s the theory, but I’ve noticed a few filaments arrive wet, with the moisture perfectly sealed in to ensure you have a poor first experience with the filament.
Above are two prints using Sainsmart transparent red TPU*, all the settings were identical, printed less than 24 hours apart. The left shows a print made with the filament right after it was taken out of the vacuum sealed bag and the right shows what the print looked like the next day, after it was stored in a watertight container* with a rechargeable dehumidifier. The filament was very well sealed in thick plastic and came with a small desiccant pack, but the 800g of TPU must have held a lot more moisture than a small desiccant pack could absorb. The results were much better after drying overnight, but it looks like there are still faint signs of moisture in the print.
So if you’re having problems with new filament, you might try drying it out to see if it helps. You can also use a warm oven for drying, you just have to be careful to avoid melting the filament or the spool.
This is what wet filament can look like when doing an air extrude, the water vaporizes forming small or large bubbles in the filament. You’ll get more oozing than usual, and there will be a rough bubbly texture to the filament. Another good indicator of a problem with moisture is if the first few centimeters extrude cleanly, then the rest of the filament extrudes messily. I believe this happens because a short section of filament near the extruder gets dried from the heat of the extruder, resulting in the clean part of the extrusion.