Crunchy prefolds! - what to do?

[knottygal]

I use GMD prefolds with Flip covers for my 3-month old son. I'm happy with the setup and washing routine. I have a tumble-dryer and not a hot-air dryer. So, I line-dry the prefolds after they come out of the tumble-dryer and they get sunned about for 2 hrs and then they go into share. The prefolds come back all crunchy and stiff. Any ideas on how to get the soft? do dryer balls work good with tumble dryers? shud I go for baby fabric softener?