In this paper, we propose the first dual-band retrodirective reflector array using Substrate Integrated Waveguide (SIW) and inkjet-printed technologies on flexible low-cost substrates, such as paper, for operability around 3.6GHz and 5.8GHz. In addition, it offers the versatility of multiband retro-directive designs potentially covering numerous RFID interrogation, sensing and communication bands, while it does not suffer from typical undesirable EM interference effects from commonly used microstrip and CPW feed-lines. The retro-directive properties of the proposed architecture have been verified through the fabrication and characterization of a benchmarking prototype.