Replacement barrier sack filter, for the Nilfisk VP300 HEPA commercial vacuum cleaner. SIMILAR to the photograph.
These shouldn't be washed, just gently vacuumed should they get dusty.
As a rule of thumb, the dustbag filters out dust greater than 50 microns, about the diameter of a human hair. This filter probably filters down to about 8 microns, and protects the HEPA filter.
The HEPA filter will filter down to .003 of a micron, and should probably be replaced each couple of years.
At the moment, delivery is capped at $20, so, how about choosing a couple of packs of bags, or other accessory, such as a replacement wand, round brush or plastic cone, from the related items below!