Now that I have determined the specs of silica gel, time to apply.
Let's dry a saturated 1kg spool of ABS. ABS water absorption is 0.2-0.4%, as I found from internet.
-> 1kg spool can hold up to 4 g of water. So, I need no less than 27 g of cat litter to dry out one spool. Or 19 g of proper silica gel desiccant.