0 to 1 lbs. per cubic ft. = Class 400
1 to 2 = Class 300
2 to 4 = Class 250
4 to 6 = Class 150
6 to 8 = Class 125
8 to 10 = Class 100
10 to 12 = Class 92.5
12 to 14 = Class 85
14 to 16 = Class 70
16 to 18 = Class 65
18 to 20 = Class 60
Over 20 = Class 50