3D printer filament is absolutely critical to the performance and output produced by your 3D printer. It's critical to find high quality replacement filament.
In an ideal world the diameter of your 3d printer filament would maintain an absolute constant diameter across the entire spool. As a manufacturer, achieving that outcome can be complicated and costly, and so there will naturally be variation in diameter of the filament. We maintain strict standards over the tolerance within which the diameter will be maintained, which prevents serious issues from arising which are usually the result of inconsistent filament diameter.
Another thing to be on the lookout for is filament roundness. It's important that the filament maintains its consistency across the entire spool. Otherwise the print quality can be affected since the imperfect filament can lead to extruder failure. Even the spool design itself plays a role in the quality of the filament which it holds.
Regardless of the manufacturer and the quality of the processes used in the production of the filament, there are environmental conditions which can impact the quality and performance of your filament. Specifically, the absorption of moisture is one of the leading causing of filament deterioration. The small water bubbles caused by the absorption of water can become an absolute nightmare. When the water bubbles are heated at the tip of the extruder they will reach the boiling point and actually explode. Needless to say, the quality of your print will be significantly impacted by this event.