Do towels become less absorbent if you use fabric softener when you wash them? I always assumed they would, since fabric softener puts a coating on the cloth, but I have no real facts to back that up, just intuition.
I would say you are right, simply because I have bought towels that say on teh label “use of fabric conditioner may make towels less absorbent”.
My PhD has yet to come through.
More to the point, is this why towels and teatowels are useless until washed?
Based on personal experience I can confim that using fabric softener on towels will make them less effective. Fabric softeners apparently are a wax based substance that coats the cloth’s fibers to make them soft. Try drying yourself with a sheet of waxed paper!
Don’t use fabric softener on your underware either!
That’s because they’re sprayed with a substance called “sizing” while they’re in the factory. It’s supposed to retard mildew. Clothes and towels often stay in boxes for a long time before they hit store shelves, and the sizing helps keep them “fresh.”
My mother used to work in a clothing stock room. She said after unpacking dozens of boxes of clothes, her hands would be coated with the chemical. She made me swear that I would always wash clothes before I wore them.
Towels, cleaning rags, cloth diapers… anything you want to be absorbant, you should definitely wash without fabric softener. If you want them to smell nice and feel softer, try a little white vinegar in the softener dispenser. (No, your laundry won’t smell like vinegar, I promise.)
As for why new towels of various types don’t work before you use them, most textile items (including most clothes as well as towels) are treated with starch to keep them looking crisp and neat during shipping and display in the store. The starch keeps the fibers from absorbing water - like fabric softener, only moreso. Washing removes most of the starch, although I often find towels aren’t at their best until they’ve had a few trips through the washing machine.
I’m allergic to the sizing chemicals that they spray on new clothes and towels. Going shopping is an itchy ordeal, let me tell you. 
I had to leave a job in a clothing stock room because of it. There is all sorts of nasty chemicals and stuff on fresh from the store clothes. I agree with the mom mentioned above. Wash before you wear.
White vinegar’s not bad, and it’s really, really cheap. However, I’ve found something I like much better, and it isn’t that expensive either.
I use RLR Laundry Treatment. Since I get it in Wally World, I assume it’s available nationwide. It’s in the laundry aisle, usually hanging on one of those strip displays. And it comes in bags of two or four treatments. It’s a white powder in a (relatively) round plastic “egg” that you open and dump into the washer.
This stuff does a great job of taking the dirt out of towels, etc., and they feel just as soft as those treated with fabric softener. What’s even nicer, it seems to keep towels going much longer. My 10 year old towels really don’t look that old, and they certainly don’t feel that old.