The perfect absorption of bending waves by thermally tunable subwavelength absorbers is analytically and experimentally demonstrated in this work for a reflection problem in beams. These absorbers are local resonators located at the end of a semi-infinite beam and consist of thin blades covered with a layer of Shape Memory Polymer (SMP), the stiffness and damping of which strongly depend on the temperature. The resonators therefore present both energy leakage from the absorbers to the beam and inherent losses thanks to the presence of the SMP. In particular, the situation in which the inherent losses balances the energy leakage is known as the critical coupling conditions and leads to the perfect absorption of the incident wave in the reflection problem. It is shown that these conditions can be simultaneously fulfilled for the different blades of the resonating system by tuning the temperature of the SMP and the geometry of the blades. The analytical results are based on the Impedance Matrix Method. The experimental validation highlights the possibility of achieving multi-frequency subwavelength absorption in the case of multi-blades configurations.