  Double polycirculant codes are introduced here as a generalization of double
circulant codes. When the matrix of the polyshift is a companion matrix of a
trinomial, we show that such a code is isodual, hence formally self-dual.
Numerical examples show that the codes constructed have optimal or
quasi-optimal parameters amongst formally self-dual codes. Self-duality, the
trivial case of isoduality, can only occur over $ \F_2$ in the double circulant
case. Building on an explicit infinite sequence of irreducible trinomials over
$\F_2,$ we show that binary double polycirculant codes are asymptotically good.
