I think one of the biggest myths concerning scrim is, the older the scrim, the better it gets. I find this is absolute rubbish. I have at least 30 scrims in the van, and I am mainly WFP. Many of these scrims are old, but none have holes in them.
You can't beat a newish, well broken in scrim. These are rougher and give a better clean on the glass. Old ones get dirty a lot quicker.
If you are trad, and do a lot of salted windows, You will find a newer scrim 10 times better.
I was using leathers and scrim to clean windows before we had squeegees in the 1950's.
We washed ours by hand in plain water, ring them out as much as you can, open them out and give them a few flicks, and use them damp.
This is the way to use scrim for hand work.
Using scrim for detailing is a different matter, you are using them to mop up the thin trails round the edges, a dry scrim will of course last longer before changing. A newer scrim, having more bulk will again last longer.
I hate tumble dried scrims, they feel far too soft for my liking. I prefer them harder, so that they form a nice pad in your hand.
As has been said above, if you put them in the washer, don't add detergent or conditioner. Dai
