Increasing expenditures for forest fire retardant and the development of more efficient delivery systems have emphasized the need for more knowledge on the transmission and retention characteristics of wildland fuels. In a series of tests, retardant was cascaded from an airplane onto arrays simulating wildland fuels. The proportion of retardant retained increased as the fuel diameter and surface roughness of individual fuel elements increased. Equations describing retention were developed and were extended to actual field situations through published research on rainfall. Retardant transmission through a tree crown was modeled; results agreed with published findings on the transmission of rain.