  Our main purpose is to describe the category of isotropic cellular spectra
over flexible fields. Guided by [6], we show that it is equivalent, as a stable
$\infty$-category equipped with a $t$-structure, to the derived category of
left comodules over the dual of the classical topological Steenrod algebra. In
order to obtain this result, the category of isotropic cellular modules over
the motivic Brown-Peterson spectrum is also studied, and isotropic Adams and
Adams-Novikov spectral sequences are developed. As a consequence, we also
compute hom sets in the category of isotropic Tate motives between motives of
isotropic cellular spectra.
