POF shrink film requires breathable holes to leak air out of the shrink film, and it is important to be exposed to the right temperature at the right time. In addition, the correct circulating wind speed is also very important in the process of shrinking the POF shrink film. The PVC shrink film does not require breathable holes to leak air out of the shrink film, as the PVC seal line is filled with small holes that act like breathable holes. Saving the process of punching breathable holes seems to be an advantage, but these small holes will actually reduce the strength of the sealing line, so that the chances of the sealing line rupture also increased. The PVC begins to contract immediately when it encounters heat, so the circulating wind of the packaging machine is not important for the PVC shrinkage film. However, the POF shrink film relies heavily on circulating wind to reach full contraction. Some simpler packaging machines can not adjust the speed of the circulating wind, when shrinking POF material will be quite difficult. When the package is wrapped by the shrink film and enters the packaging machine, the heat will make the air in the shrink film expand, when the shrink film begins to contract, the air from the breathable hole leakage pressure, to prevent the shrink membrane from breaking.