Transmission (e^−τ) as a function of wavelength around Lyα due to the neutral IGM and local absorbers for high resolution (R ≳ 1000, left panels) and convolved with the resolution of the prism (right panels). Top panels: Transmission for a source at z = 10. The thick grey line shows the transmission expected in the fully neutral IGM (Section 2.1.1). Dashed coloured lines show the absorption profiles expected for local absorbers in an ionized IGM (Section 2.2). Solid coloured lines show the profiles for the combinations of both local absorbers and neutral IGM. For N_H I ≲10^20.5 cm⁻² the neutral IGM dominates the damping wing profile. For higher column densities N_H I ≳ 10²² cm⁻², the shape becomes dominated by the local absorption, though the neutral IGM causes more absorption at redder wavelengths than a local absorber alone. Bottom panels: Neutral IGM damping wing at z = 6, 10, 14 (grey solid lines) compared to only local absorption (dashed coloured lines, same as top panel). By z ∼ 14 the IGM damping wing becomes similar in strength to a N_H I ≳ 10^21.5 cm⁻² local absorber.