call sl2-tiling a filling of the discrete plane by elements of a ring (the coefficients) in such a way that each connected 2 by 2 submatrix has determinant 1. similar objects have been studied by coxeter and conway; they call them frieze-patterns. given a bi-infinite word on {x, y}, interpreted as a path in the discrete plane, called the frontier, put 1s at its vertices. then one may uniquely complete this picture to an sl2-tiling; it turns out that the coefficients of the tiling are all positive integers; we prove this by giving explicit matrix product formulas for these coefficients. our constructions are motivated by the so-called "frises", associated to acyclic digraphs. in a joint work with i. assem and d. smith, we showed that the sequences of the frise all satisfy a linear recursion if and only if the digraph is a dynkin diagram, or an affine diagram, with an acyclic orientation.