Mechanical networks of fibres arise on a range of scales in nature and technology, from the
cytoskeleton of a cell to blood clots, from textiles and felts to skin and collageneous tissues.
Their collective response is dependent on the individual response of the constituent filaments
as well as density, topology and order in the network. Here, we use the example of a lowdensity synthetic felt of athermal filaments to study the generic features of the mechanical
response of such networks including strain stiffening and large effective Poisson ratios.
A simple microscopic model allows us to explain these features of our observations, and
provides us with a baseline framework to understand active biomechanical networks.