Comparison of collisional lifetimes for different materials and porosities. The solid line represents the original Grün et al. (1985) lifetimes: crosses demonstrate the particle sizes used in this model. The squares provide these collisional lifetimes when multiplied by the F_coll given in Table 1, which varies with particle size. This is compared to recalculations of the collisional lifetimes using the method of Grün et al. (1985), but using the experimental results of Nakamura et al. (2015), which demonstrate how they are variable with particle material and porosity (dashed and dot-dashed lines). Finally, the Poynting-Robertson lifetimes (dotted line) demonstrate how the dominance of Poynting-Roberston drag or collisional shattering isdependent on particle composition and structure.