Depends on your coop. I have found shavings are easier for them to kick around and dehydrate the poop better than straw, however, it's messier and dustier. It's quick and easy to rake out hay and replace it, but for longer term, shavings smell better and they can churn the poop around. I guess it's up to what works best for you! My girls did prefer straw in the nesting boxes to shavings as they could fashion cool nests with it. Try one and then the other! See what you like or don't. Do you have a picture of your coop? It makes it easier to see how much moisture could get in and how much you might need.