  Viscosity of fluids is strongly system-dependent, varies across many orders
of magnitude and depends on molecular interactions and structure in a complex
way not amenable to first-principles theories. Despite the variations and
theoretical difficulties, we find a new quantity setting the minimal kinematic
viscosity of fluids: $\nu_m=\frac{1}{4\pi}\frac{\hbar}{\sqrt{m_em}}$, where
$m_e$ and $m$ are electron and molecule masses. We subsequently introduce a new
property, the "elementary" viscosity $\iota$ with the lower bound set by
fundamental physical constants and notably involving the proton-to-electron
mass ratio:
$\iota_m=\frac{\hbar}{4\pi}\left({\frac{m_p}{m_e}}\right)^{\frac{1}{2}}$, where
$m_p$ is the proton mass. We discuss the connection of our result to the bound
found by Kovtun, Son and Starinets in strongly-interacting field theories.
