  In high energy collisions of heavy-ions, experimental findings of collective
flow are customarily associated with the presence of a thermalized medium
expanding according to the laws of hydrodynamics. Recently, the ATLAS, CMS and
ALICE experiments found signals of the same type and magnitude in
ultrarelativistic proton-proton collisions. In this study, the state-of-the-art
hydrodynamic model SONIC is used to simulate the systems created in p+p
collisions. By varying the size of the second-order transport coefficients, the
range of applicability of hydrodynamics itself to the systems created in p+p
collisions is quantified. It is found that hydrodynamics can give
quantitatively reliable results for the particle spectra and the elliptic
momentum anisotropy coefficient $v_2$. Using a simple geometric model of the
proton based on the elastic form factor leads to results of similar type and
magnitude to those found in experiment when allowing for a small bulk viscosity
coefficient.
