PakShak said:
“white vinegar� is a natural fabric softener which could be the reason why the towels are loosing it’s absorbency. Too much of a good thing “vinegar� in this case might be the root of the problem. Over time (few months) with frequent washes, the residue left behind by vinegar in the towel is most likely repelling the water instead of absorbing it.
As a newbie on this site, I really hate that one of my initial posts is in disagreement with Ranney, who I recognize as an expert on towels! But I think the above advice may be a bit off target. As long as your washer is working correctly, using vinegar in your rinse should cause absolutely no problems with MF. In fact, it is one of the best things you can do to clean your towels effectively.
Vinegar is a "natural fabric softener," sure, but not in the sense of the commercial fabric softeners. The latter work by using a chemical surfactant that coats fibers, making them feel softer and eliminating static. Distilled White Vinegar, OTOH, is a rinse aid that helps the washer rinse out the soap in the water and on the towel. It will not build up on fibers. Also, if you have a "second rinse" option on your washer, use it. When you do this, the DWV is used in the first rinse and the second rinse is just water. You can never rinse enough.
There are several things that could be "wrong" with what the OP is doing. He may not have a very good washer that fully cleans the old product off the towels. He may be using too much detergent and/or a detergent with a fabric softener additive. He may be seeing transfer of fabric softener or some other crud from his washer or (more likely) his dryer. Many people use dryer sheets, and those leave a waxy residue inside the dryer. To clean your washer, just run a cycle with no clothes, a cup or so of Cascade dishwasher detergent, and a cycle that fills the drum with hot water. Note this is for TL washers. For FL, read your user manual about how much soap to use.
To wash MF towels -- or any towels, frankly -- you should use a good detergent and a vinegar rinse. Tide is a perfectly acceptable detergent. For a small load of MF towels, use far less than you would use for regular clothes washing. Use the HOTTEST water you can (this is key). Many advanced FL washers have secondary water heaters that allow for a "sanitary" cycle with near-boiling water. Use it. Using very hot water will help lift all the crud off your towels to be rinsed away.
Finally, it's also possible the OP expects too much from MF towels. Most are not that absorbent to begin with.