Female seeds ice is extremely dense,rock hard to be exact.Blockhead is another dense indica.You're going to find besides low flowering humidity(I set my dehumidifier for 40% RH),its mainly going to be strain dependent.Serious seeds AK47 or female seeds grapefruit are good examples of strains that are rather fluffy no matter the environment,this is what I've found.The indica's will be mostly dense while indica-sativa hybrids and sativa's will not be dense