As an alternative to traditional hot-mix asphalt paving, bitumen foaming technologies have been extensively used in road recycling over the last decades. However, much more work on the use of foam-enhancing chemical agents is needed. This research deals with the influence that temperature and processing protocol exert on the bitumen foaming process promoted by a poly(propylene glycol) functionalized with a polymeric 4,4'-diphenylmethane diisocyanate. Likewise, rheological and microstructural characterizations have been carried out on the modified bituminous residues obtained after foaming. From the experimental results obtained, it may be concluded that reactive isocyanate-based polymers can be used to obtain foamed binders with different foamability and stability characteristics. On the other hand, both foaming and bitumen modification are seen to occur simultaneously, as a result of bitumen/polymer reactions involving water. Finally, dynamic shear tests and atomic force microscopy observations reveal very different degrees of modification, which depend on the colloidal features of the as-received bitumen.