PUL is not difficult fabric to sew with, but it does present its unique challenges.
Most challenging is that the PUL side is often fairly “sticky” – it doesn’t tend to want to easily glide through the sewing machine. This can be overcome by using a teflon sewing machine foot, like this one: http://www.amazon.com/Generic-20034-Teflon-Foot/dp/B0015S8AW6
Some people also report success with carefully putting some tape over their regular sewing foot to make it more glide-y. Another solution is to just always sew with the PUL side down, contacting the feed dogs instead of the presser foot. This does not always help, though!
I think the second most challenging aspect of PUL is that it’s hard to correct mistakes. The needle holes don’t disappear – they are there forever. So, think before you sew, and rip stitches out with care!
For the same reason, be careful with pinning your PUL items together before sewing. Many people choose to use clips instead of pins, but a lot of us just simply pin in the seam allowance.
And, of course, the most common problem in using PUL is producing something that leaks. Be sure to use a high quality, 100% polyester thread. Make as few holes as possible (larger, longer stitches). Don’t pair the PUL with a regular 100% cotton fabric (it’s certainly possible to make a leak-free diaper with cotton as an outer, decorative layer, but that type of diaper is more likely to experience leaks.
(note: we are not responsible for sewing projects that don’t turn out how you wanted them to!)