I devise a method to separate low-z Lyα absorbers into void, and non-void clouds. The strong difference between void and non-void EW distribution functions enables a phenomenological definition of voids. I find the filling fraction of voids in the universe is f v = 0.86-0.11 +0.05, greater than voids defined by galaxies (f v ≲ 0.5). I show that they cannot be explained as diffuse and expanding with the Hubble flow. Instead I model clouds as based on subgalactic halos whose baryons expand following reionization. Results of modeling show that only isothermal massive halos produce absorbers consistent with observations; NFW halos are not massive enough to restrain the evaporation of baryons, and produce no detectable absorption systems. A halo velocity distribution with slope parameter α = -1.95, and normalized to φ*V = 0.05φ* can explain the observed distribution of void clouds.