  Although coveted in applications, few materials expand when subject to
compression or contract under decompression, i.e., exhibit the negative
compressibility phenomenon. A key step to achieve such counterintuitive
behaviour is the destabilisations of (meta)stable equilibria of the
constituents. Here, we propose a simple strategy to obtain negative
compressibility exploiting capillary forces both to precompress the elastic
material and to release such precompression by a threshold phenomenon -- the
reversible formation of a bubble in a lyophobic flexible cavity. We demonstrate
that the solid part of such metastable elastocapillary systems displays
negative compressibility across different scales: hydrophobic microporous
materials, proteins, and millimetre-sized laminae. This concept is applicable
to fields such as porous materials, biomolecules, sensors and may be easily
extended to create unexpected material susceptibilities.
