Granules that pick up moisture mean surface defects in injection moulding; granules that pick up dirt mean a scrapped batch. How the raw material is kept until it reaches the machine decides the quality of the part that comes out. Some polymers draw moisture from the air on their own; those that don't can still get wet when cold packaging sweats in a warmer space. When dust, fibre or a stray granule of another grade gets in, the problem often only shows at the machine, in the finished part. So the aim in storing plastic granules is to keep the material as it arrived: a warehouse cannot improve the product, only stop it deteriorating.
Form matters too. 25 kg sacks arrive palletised and stretch-wrapped; as long as the wrap stays intact, the pallet moves as one unit. A sack's weak point is its seam, and a sack that splits along the seam can empty unnoticed inside the stack. Big bags are lifted by their loops; if the load on the loops is uneven, the bag can tear. An octabin's cardboard body is vulnerable to damp and crushing, so it stays within its own stacking limit and is not set down on a wet floor. The wrong attachment or one layer too many tears the packaging, and the granules inside are left exposed.
If different lots of the same product get mixed, the source of a later problem can never be traced. That is why every lot has its own rack location and every movement is scanned on the handheld terminal. If a complaint comes up about a lot, the records show the day it came in, the location it sat at and when it left. In polymer storage, mixing costs more than the quantity mixed: the whole lot becomes suspect.