We (a small group of scientists from various LAr experiments) have measured the longterm stability of a Poly(ethylene 2,6-naphthalate)-based wavelength-shifting reflector as a potential candidate to substitute TPB in large LAr detectors in a 2 tonne-cryostat at CERN. The preprint is on the arXiv today: arXiv:2411.17934 and will be published as proceedings of the LIDINE 2024 conference.