DOW USM - Universal Support Material is water-soluble
It works with a number of common 3D printing filaments to make complex parts turn out better, when used with the dual Extruder printers.
Spool net weights are net weight of the filament, but because the filament is less dense than most, the net weight on a spool is less than typical sizes.
An 375g net weight spool holds about 480 ft. of filament, about the same as a 454g spool of ABS. It therefore produces the same extrusion volume as roughly that 454g of ABS would. Visually, it looks like a 454g spool.
Though the price for a spool may seem unusually high, the typical cost per part of support material is not necessarily a large cost.
Most parts can be printed with just a small "interface" layer of USM between the main plastic used for the part and the main bulk of support that can also be printed in the same material as the part. So the USM becomes only e.g. 10% of the total plastic being extruded.