The music manuscripts, 1927-1986, of Mansel Thomas, comprising music for male voice choirs, mixed choirs, youth and female voices, solo songs, and instrumental compositions. They consist mainly of Christmas music, hymn-tunes, liturgical music, arrangements of Welsh traditional melodies, secular music and solo songs, the majority of which have been published by the Mansel Thomas Trust and the Cwmni Cyhoeddi Gwynn Publishing Company. Some manuscripts are in the hand of copyists and may contain later notes and additions.

Manuscript scores of orchestral music by Mansel Thomas, comprising arrangements of Welsh folk songs, other tunes, incidental music; music for brass bands and ensembles (including trio, quartet etc.).

A miscellaneous collection of orchestral parts from the library of David Lewis.

Papers created and compiled by Peter Reynolds in his work as a composer of musical works, a writer and critic, and his lecture notes. Musical compositions include full orchestral scores, parts works, arrangements, draft works and sketches. Research papers and notes covering musical compositions, composers and artists, accumulated during his research for the writing of programme notes and his copywriting. Some of these files contain historical items collected for reference. Subject files and a large collection of concert and event literature. Teaching notes for lectures at WCMD and his composers workshops.
Two boxes of audio material have been transferred to The National Screen and Sound Archive of Wales.