Yep, they are.. that is why I am not really bothered throwing a couple out when they get so gunky.
I do exactly that, I buy a box of them at a time and they usually last me a year or so on the farm. I try to rewash the ones that do not get too bad. Some of them would clog the washing machine if I tried, and funk it up for future washes.
I've seen them say you shouldn't run them through the dryer, but I haven't had a problem with them so far. Yeah, they might stick to other stuff, but it doesn't wreck them. I keep a couple in my truck at all times for camping and things like that.