Hydrogenated polymorphous silicon (pm-Si:H) is a new material obtained by plasma-enhanced chemical vapour deposition by running the plasma close to powder formation. Preliminary studies have revealed the presence of silicon nanocrystallites embedded in an amorphous matrix but only in a limited range of deposition conditions. In this work we have investigated the structural properties of such films by means of spectroscopic optical measurements. The analysis of transmission spectra in the transparent region has shown that pm-Si:H films have indeed a more ordered structure than state-of-the-art hydrogenated amorphous silicon (a-Si:H) films. This has been observed in the whole range of deposition conditions leading to pm-Si:H films. On a final point the implication of structural properties on the excellent optoelectronic properties previously reported in pm-Si:H films is discussed.