BuildingMaterials:Balsa,PeckContest Traditional contest balsa that has been individually weight and sorted. Density is based on nominal sheet thickness (i.e. 1/16, 1/8 etc.) and thickness is not calculated per individual sheet. Badly wavy & warped sheets are culled. NOTE: Lighter density balsa will have more stains, waviness, and minor flaws then heavier wood. This is normal and must be accepted if ordering.Density categories are as follows: 4# = 4.00 > 4.99, 5# = 5.00 > 5.99, 6# = 6.00 > 6.99If you are looking for our best World Class grade balsa that is individually graded and tested click this link to order Tru-Weight Indoor Balsa