  The longitudinal structure function in deep inelastic scattering is one of
the observables from which the gluon distribution can be unfolded.
Consequently, this observable can be used to constrain the QCD dynamics at
small $x$. In this work we compare the predictions of distinct QCD models with
the recent experimental results for $F_L(x,Q^2)$ at small $x$ and low $Q^2$
obtained by the H1 collaboration. We focus mainly on the color dipole approach,
selecting those models which include saturation effects. Such models are
suitable at this kinematical region and also resum a wide class of higher twist
contributions to the observables. Therefore, we investigate the influence of
these corrections to $F_L$ in the present region of interest.
