  In the present paper, we investigate the collapsed phase of the interacting
partially-directed self-avoiding walk (IPDSAW) that was introduced in Zwanzig
and Lauritzen (1968). We provide sharp asymptotics of the partition function
inside the collapsed phase, proving rigorously a conjecture formulated in
Guttmann (2015) and Owczarek et al. (1993). As a by-product of our result, we
obtain that, inside the collapsed phase, a typical IPDSAW trajectory is made of
a unique macroscopic bead, consisting of a concatenation of long vertical
stretches of alternating signs, outside which only finitely many monomers are
lying.
