Low density additives and methods of making said additives for composite materials are provided. The low density additives have at least a partial or complete water repellant property that reduces moisture migration, absorption, and retention within a composite material in which it is incorporated into. Active sites are engineered onto the surface of the low density additives to enhance bonding of the additives within a composite matrix. Reduced water movement and enhanced bonding lead to an increased strength and durability performance for a composite material comprising such additives. Composite materials incorporating one or more engineered low density additives as also provided, such composite materials having enhanced strength and durability. Such composite materials may be made from a Hatschek process. The composite materials may be further used as interior and exterior building products.