Hey Growmie ...
There are actually several things that can cause airy buds but the five most likely scenarios for your buds ending up airy are improper lighting, too high or too low temperature, nutrients being too much or too little, poor airflow, or root problems. You also have to take in the fact that it could be genetics also.
Hopefully, this was helpful and remember ..."Happy Growing" and "Free your mind one puff at a time".
Mr_Weeds_Autos.