Chip-in-plastic (CIP) packages using three types of ACFs have been investigated as a flexible display package solution for high-definition (HD) display applications. By optimizing the CIP packages, higher flexibility could be achieved compared with the chip-on-plastic packages. Three types of ACFs were prepared: the conventional ACFs, nanofiber ACFs, and anchoring polymer layer (APL) ACFs. The electrical properties and bending reliability of CIP packages using these ACFs were evaluated. For electrical characteristics, unlike the conventional ACFs, the nanofiber and APL ACFs showed a 100% insulation property at a 20-mu m pitch. The rate of increase in contact resistance after a dynamic bending test of 100 000 cycles at a 15-mm bending radius was 0.6%, 0.9%, and 1.1% for the APL, nanofiber, and conventional ACFs, respectively. The APL ACFs showed the most stable resistance changes during a dynamic bending test. Specifically, they showed the highest modulus of 1.8 GPa and the lowest accumulated plastic strain. Therefore, it was confirmed that the CIP packages using APL ACFs are the most suitable package structure for flexible display driver IC packages and HD display applications.