Buds - Difference Between Compact and Fluffy

light really plays a major factor in bud density

its mostly strain, but yes, high phosph can help density, and deffinately higher wattage light.

When I grew with cfls I got mostly fluffy buds, nice size but not much weight. Now that I'm using mh/hps my buds are much bigger and heavier

Cooler temps?

you get your lights to close and you'll end up with " airy " buds too..

nope that's genetics

humidity also plays a major role in bud density.
lower the humidity and your buds should be denser.
plants produce resin as "sunblock" to protect its self from, in my case, twin suns

High temps also cause airy buds

Good to hear! Where are they sitting?