I have to disagree with Karla and Jess. I'm the one who originally suggested hari conditioner (can't even remember how long ago it was now, LOL!) becuase that's waht I do for scrathy wool, and it's always worked for me. Wool is just sheep hair,a fter all
I'll explain though, why Karla's theory isn't quite on target, and why you can use conditioner on (unfelted) wool without it stretching. First, a bit on how wool felts. Sheep hair, when exposed to temperature changes and agitation, will grab on to each other and basically knot and twist around each other, thus shortening the overall fibers until they are one big mated, knotted mess (AKA, felt!)
Hair conditioner works to stretch felt, becuae essentially what it does is help to coat the hairs so that you can gently pull apart the knots without breaking the fiber. It works essentially the same as that spray-on detangler stuff you can use on your kids :LOL
Now, it doesn't make unfelted wool stretch because in unfelted wool, the fibers aren't matted and knotted/tangled, so there isn't much to stretch out. Granted, the fibers are twisted together to make the yarn, but they are not enmeshed nearly like they are in felt.
So, in short, you can use hair conditioner on wool that is scratchy to try to make it softer. However, IME, the Bartlett's yarn gets much softer all on it's own after a few washes and general wear
nak a teething babe, so forgive typos!