Over time, towels build up detergent and fabric softener, leaving them unable to absorb as much water and smelly. Recharge them by washing them once with hot water and 1cup vinegar, then a 2nd time with hot water and half cup baking soda. This strips the residue and leaves them fresh and able to absorb more water again. Works like a charm!
Clean Towels . . . works great . . . found another suggestion to add 2 tsps dawn dishwashing liquid to vinegar load. Doesn't seem necessary, but good to know. Be aware - dryer sheets build up residue on towels over time.