  Symmetries crucially underlie the classification of topological phases of
matter. Most materials, both natural as well as architectured, possess
crystalline symmetries. Recent theoretical works unveiled that these
crystalline symmetries can stabilize fragile Bloch bands that challenge our
very notion of topology: while answering to the most basic definition of
topology, one can trivialize these bands through the addition of trivial Bloch
bands. Here, we fully characterize the symmetry properties of the response of
an acoustic metamaterial to establish the fragile nature of the low-lying Bloch
bands. Additionally, we present a spectral signature in the form of spectral
flow under twisted boundary conditions.
