We present XMM-Newton observations of the Seyfert 1 AGN H0557-385. We have conducted a study into the warm absorber present in this source, and using high-resolution RGS data we find that the absorption can be characterised by two phases: a phase with log ionisation parameter xi of 0.50 (where xi is in units of ergs cm/s) and a column of 0.2e21 cm^-2, and a phase with log xi of 1.62 and a column of 1.3e22 cm^-2. An iron K alpha line is detected. Neutral absorption is also present in the source, and we discuss possible origins for this. On the assumption that the ionised absorbers originate as an outflow from the inner edge of the torus, we use a new method for finding the volume filling factor. Both phases of H0557-385 have small volume filling factors (< 1%). We also derive the volume filling factors for a sample of 23 AGN using this assumption and for the absorbers with log xi > 0.7 we find reasonable agreement with the filling factors obtained through the alternative method of equating the momentum flow of the absorbers to the momentum loss of the radiation field. By comparing the filling factors obtained by the two methods, we infer that some absorbers with log xi < 0.7 occur at significantly larger distances from the nucleus than the inner edge of the torus.
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