Filter bags- ugh! Get a cyclone!
Sorry, now that I've got that out of my system. Before we knew about the dangers of fine dust to the lungs, filter bags were used on all DC's mainly to trap wood chips (and let air pass)- to help keep a shop "cleaner." They are a strange, no win device- they actually work better* when caked with dust . . . up to a point, then when they get too caked, suction suffers. *They do a better job filtering fine dust when already caked with dust. So the bottom line is you need to decide when you have lost too much suction.
Conventional wisdom is that for safety sake and to protect your lungs, it is best to
get as much dust at the source- at the machine. That means maximum DC volume and velocity. On the other hand, while they stop chips and large dust particles, typical filter bags (depending on micron rating) will actually let pass a lot of fine, most dangerous and unhealthy dust, when they are clean. You need to think about why you have a DC - for a clean shop or a clean
and healthy shop.
Bill Pentz's web site has some extensive discussions of all this on his site.
As far as your question, the only other factor, is what washing will do to the fabric weave and filtering ability. I frankly don't know.
Now, without spending money on a cyclone and a cartridge filter (which filter MUCH, MUCH better than fabric bags) a solution is to put the DC outside where escaping fine dust won't affect your lungs, then keep the bags clean.
