In ΛCDM, the transverse width of cosmic web filaments is expected to reflect the balance between gravitational collapse and background expansion, leading to relatively simple scaling relations between filament thickness and the mass (or linear mass density) of halos embedded within them, as seen in N-body and hydrodynamic simulations (Bond et al. 1996; Zhu et al. 2024). Observations and detailed simulations, however, often find either systematically different widths at fixed mass, nearly scale-invariant widths over wide mass ranges, or more complex trends and scatter than the basic halo- and shear-based ΛCDM picture predicts, suggesting missing environmental physics, baryonic effects, or limitations in the standard model’s treatment of filament structure (Cautun et al. 2014; Zhu et al. 2025).