If you are talking the bagged stuff, I like wood chips or big shavings better if you can't get sand or gravel, they hold up better than bark and don't mold as easily. If you mean you are chipping it yourself, I don't worry if it is mixed wood/bark, I do try to avoid getting any black walnut though.
I contacted my local council
Got wood chips today
5 happy girls
Apart from rain all day
Im such a mum actually worried they were goin to bed wet
So packed out the coop with more shavings and straw