  In this letter we use the Carath\'{e}odory's approach to thermodynamics, to
construct the thermodynamic manifold of the Hayward black hole. The Pfaffian
form representing the infinitesimal heat exchange reversibly is considered to
be $\delta Q_{\mathrm{rev}}\equiv {\rm d}r_s-\mathcal{F}_H {\rm d}l$,
previously obtained by Molina \& Villanueva \cite{fmv20}, where $r_s$ is the
Schwarzschild radius, $l$ is the Hayward's parameter responsible for the
possible regularization of the Schwarzschild black hole, and $\mathcal{F}_H$ is
the intensive variable called the Hayward's force. By solving the associated
Cauchy problem, the adiabatic paths are confined to the non-extremal manifold,
and therefore, the status of the second and third laws are preserved.
Consequently, the extremal sub-manifold corresponds to the {adiabatically
disconnected} boundary of the manifold. In addition, the merger of two extremal
Hayward black holes is analyzed.
