Polymers were one the first materials to be processed by ultrafast lasers. However, the nature of absorption for near-infrared laser beams is not fully understood, and therefore, it remains challenging to process polymeric materials with high energy-efficiency. In this study, the pulse-to-pulse evolution of optical properties (reflectance, transmittance, absorptance) of polypropylene (PP), which is a polymeric material widely used in many industrial applications, is determined by performing time-resolved measurements from pulse to pulse for a wide range of pulse energies. The goal is to differentiate between linear and nonlinear absorption in different laser-matter interaction regimes, and select the processing condition that yields the highest energy-efficiency. The experiment is performed by recording the reflection and transmission of each laser pulse in an ellipsoidal mirror - based setup, which enables the collection of scattering reflection with nearly full coverage. Absorption is calculated from the experimental data, and a model consisting of linear and nonlinear absorption is used to analyze the results. It is found that PP undergoes dramatic morphological change from pulse to pulse, which is accompanied with changes in optical properties that call for the tuning of laser condition in order to fully utilize the laser energy. Our results could be helpful for increasing energy-efficiency in ultrashort-pulsed laser processing of polymers towards high-throughput operation.