Unusual instrumentation and unusual performance techniques, including elements of improvisation, are also important features of his work. In 1998 he composed "X-ist", a piece for IST (the Improvising String Trio, consisting of harp, cello and double-bass). It was described by reviewers as a "frighteningly frantic" and "challenging" piece. "X-ist" uses a graphic score and includes written directions to the players that act as "creative stimuli", containing notes and motifs to be followed. The piece also requires the cellist and double-bassist to tap their instruments, as well as use normal playing methods. Another piece requiring improvisation by performers was his commission for the 2001 Bangor New Music Festival, , which was written for ensemble (saxophone, guitar, harp, keyboard, cello, piano) and optional dancer. In his performing notes, Puw describes the pieces as a "stimulus for musical improvisation" in which any notes, normal or extended musical techniques and/or percussive effects may be applied. has two contrasting sub-sections, a and b, arranged in the form a-b-a-a-a-b-a-b to match the Welsh poetic measure of the same name, with the strings playing calmly in the "a" sections, and saxophone and keyboard (gradually joined by the other instruments) playing in a more lively manner in the "b" sections. The musicians and the dancer are required to react to each other's contributions in each section to create a "multi-media" experience.