Im having major foxtail action right now, apparently its from high heat, which makes sense for me because my room temps are in the 80s right now due to the heat wave.
i was thinking about buying a portable AC.
another thing i noticed was that only my top colas are foxtailing, maybe perhaps they are under heat stress from being too close to the lights. my mid level buds are all nice and round with no foxtailing.
Foxtailing can be attributed to both environmental and genetic factors. Indeed, high temperatures in the canopy will cause foxtailing and create "airy" buds but some strains will foxtail on their own despite temperatures.
My Jack Herer x White Rhino foxtails a bit. I've seen the trait repeatedly and I would say in my case it is due to sativa influence in the different strains. I don't see it as an indication of heat stress (even if it may be), as the bud generally ends up being mind-melting.
I usually grow very sativa dominant hybrids such as kali mist or jack herer. (The few landrace sativas I did grow, foxtailed heavily.)