Here's some excellent information from a FAQ on Adam's Forums:
Your microfiber should be cleaned after every use. While it might be tempting to let that drying towel sit and use it again next weekend you run the risk of contamination causing swirls or letting something set into the towels that will be more difficult to remove later. Cleaning microfiber is usually the least enjoyable part of a detail, but in the end staying on top of your laundry just ensures that your towels will be at their best and ready when you are.
The option to avoid, and one incorrectly recommended by amateurs all over the web, are 'delicate' detergents like Woolite. Products in this category are lacking in the areas needed to really remove all the residues found in your towels. We're dealing with tough residues embedded deep into very tiny fibers - use a detergent capable of getting the job done. While microfiber is important, and should be cared for appropriately, it is fairly durable stuff and can handle stronger detergents to make sure they are 100% clean. Weaker detergents will continually leave behind a small amount of detailing contamination, leading to a slow buildup and eventually hampered performance.
CLEANING MICROFIBER TOWELS
- Always separate your dirtiest towels, like those used to clean wheels or for metal polishing, from your 'good' plush and drying towels to avoid cross contamination and wash them in separate loads.
- Keep cotton and other materials out of the wash loads. Wash microfiber only with other microfiber.
- Use a dedicated microfiber detergent like Microfiber Revitalizer & Brightener, NO FABRIC SOFTENER.
- Set washer to a warm water setting. Some heat is required to break down waxes and polishes. Cold settings will not clean towels as effectively.
- If your washer is equipped with an extra rinse cycle, use it. This will make sure as much of the contamination and remaining soap is removed from the towels as possible.
- Microfiber can be machine dried if you prefer, use a low heat setting and NO DRYER SHEETS. Air or line drying is also an option, be sure to do this somewhere the towels cannot be contaminated with dust or lint.
MICROFIBER PADS & APPLICATORS
- Just like with towels, separate any extremely dirty or contaminated pads from the group and wash separately to avoid cross contamination.
- Wash pads and applicators separate from towels. The foam backing and velcro can become snagged and damaged during agitation by a towel in the same load.
- Use a brush to break up heavy, caked in, polish residues on pads before washing.
- Use Microfiber Revitalizer & Brightener.
- Set washer to a warm setting, not hot. Pads have a glue membrane that is sensitive to high heat so stick to warm wash water settings.
- Air dry all pads and applicators on a wire rack to maximize airflow and expedite drying.
HEAVY STAINS AND CONTAMINATION:
No matter what there is going to be occasions where a towel becomes extremely contaminated or stained from either something you removed from a vehicle (grease, oil, tar, etc) or it becomes saturated with a product to the point there is some discoloration. In these situations pre-treating or at the very minimum pre-soaking the microfiber to keep these stains from setting in is key. Obviously, you can't stop mid-detail and clean your microfiber accessories, so here are some quick tips to help with heavier contamination on the fly.
Pre-treat any towel that becomes heavily soiled with grease, oil, brake dust, etc - spray liberally with All Purpose Cleaner or Microfiber Revitalizer. Soak the heaviest contamination and rub the towel against itself to agitate, then set aside for cleaning later.
Pre-soak towels to help start the cleaning process long before you get around to doing your detail laundry. Prep a separate bucket with clean water and add 2-3oz of Microfiber Revitalizer. As towels become too dirty to continue using toss them into the pre-soak bucket. Place a grit guard, upside down and ON TOP of the towels after they've been put in the mix to hold them in the solution as they try to float to the top.
For microfiber polishing pads or applicators use a stiff brush, like the pad conditioning brush, to break up residues before they harden and set in. Pads can also be added to your pre-soak bucket if desired.
If a towel ever becomes so contaminated that it doesn't wash clean, it may be time to retire it to a new job. Rotate towels that have been heavily stained to less delicate tasks.