Single Point Incremental Forming (SPIF) has received considerable attention recently due to advantages such as partshape-independent tooling, higher formability and higher process flexibility as compared to conventional forming. While significant research has been performed on SPIF of metals, recent work has also shown the feasibility of using SPIF for cold-forming of thermoplastic polymer sheets. However, the effects of incremental depth and part shape on the modes of failure during polymer SPIF have rarely been investigated. This paper examines the effects of part shape and incremental depth on the formability and failure modes in polymer SPIF. It is shown that greater incremental depths result in greater formability in polymer SPIF. Furthermore, it is shown that increasing the rate of change of the wall angle with the Z depth of the part increases the maximum formability achievable using a given incremental depth. At the same time, it is observed that this dual advantage of greater formability and reduced forming time, possible with higher incremental depths, is limited by the occurrence of sheet wrinkling when the incremental depth becomes too high. Additionally, the dependence of sheet wrinkling on the overall shape of the part being formed is also shown.