The adhesion and friction behavior of soft materials, including compliant brushes and hairs, depends on the temporal
and spatial evolution of the interfaces in contact. For compliant nanofibrous materials, the actual contact area individual fibers make
with surfaces depends on the preload applied upon contact. Using in situ microscopy observations of preloaded nanotube hairs, we
show how nanotubes make cooperative contact with a surface by buckling and conforming to the surface topography. The overall
adhesion of compliant nanohairs increases with increasing preload as nanotubes deform and continuously add new side-wall contacts
with the surface. Electrical resistance measurements indicate significant hysteresis in the relative contact area. Contact area increases
with preload (or stress) and decreases suddenly during unloading, consistent with strong adhesion observed for these complaint
nanohairs.