<p>Brominated butyl rubber (BIIR) is extensively utilized in products such as tyres and biomedical products owing to its excellent elasticity and gas barrier properties, while the recycling of the end-of-life BIIR products remains a challenge because of the existence of a covalent cross-linked network. Herein, direct upcycling of unmodified waste BIIR is achieved through a nanoparticle-mediated interfacial cross-linking strategy, circumventing chemical modification or degradation of its polymer structure. Specifically, pyridyl-functionalized silica nanoparticles (SiO₂-Py) are synthesized and utilized to crosslink the bromine atoms in waste BIIR with those of fresh BIIR to reconstruct the crosslink network without altering the original sulfur-vulcanization network of waste BIIR. The resulting composites exhibit a dual interpenetrating network structure comprising the sulfur-vulcanized network and the bromine-pyridinium crosslinked silica-rich network, which endows the composites with exceptional strength and toughness. As a result, the waste BIIR from the discarded bicycle inner tyres is successfully upcycled into high-performance BIIR composites, demonstrating superior tensile strength (∼14 MPa), toughness (∼60 MJ m⁻³), and ultra-low air permeability (8.78×10⁻¹⁵ cm³ cm/(cm² s Pa)), significantly outperforming the original material from bicycle inner tubes. This work presents a scalable and effective solution for BIIR waste recycling, offering great potential for advancing the sustainable development of the rubber industry.</p>