Nanomechanics has been slow in entering nanotechnology because of extreme conditions resulting from scaling. This is an issue in particular for polymers, although widely used in macroscale applications. Highly repetitive nanoscale deformation cycling in combination with excellent shape retention and thermal stability is demonstrated. While generic principles described are pertinent to a range of applications, this demonstration is made on the example of polymer media in high-density data storage. The information, represented as indents, is written and erased using a heated tip. A highperformance polymer with a flexible aryletherketone backbone is designed with phenylethynyl crosslink chemistry. After optimization of crosslink density and topology, unprecedented performance is achieved in all relevant metrics. Demonstrations of endurance and retention are performed at 1 Tb in-2 density, showing 108 write cycles using the same tip, 103 erase cycles and 3 X 105 read cycles of the media, and extrapolated to 10 years of retention at 85 °C. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA.