Here is a tip that a ballet teacher shared with me recently regarding tulle
Not all tulle is created the same. If you're buying tulle to make a tutu, be sure to buy what you need all at the same time because dye lots and thread thicknesses vary.
Narrower thread = softer tulle
Small diamond hole nylon tulle makes soft tutus. However, softer tutus have been known to not last as long over time.
A good resource for tulle is Gifts International.