A new method to probe nanoscale structure (pores, defects, and damage accumulation) for microporous coordination polymers during adsorption of guest molecules (see figure, representing CO2 sorption with definitive evidence of residual porosity) or undergoing thermal degradation is demonstrated using positron annihilation. Structural features invisible to traditional X-ray diffraction and gas-adsorption techniques are revealed, demonstrating a new capability for porous materials characterization.