Abstract. Let K be a field and let / 6 K[ [xι,x 2 , . ,x r ]] and g 6 #[[2/1,2/2, , y s ]] be non-zero and non-invertible elements. If X (resp. Y) is a matrix factorization of / (resp. g), then we can construct the matrix factorization X §> Y of /-+• g over K [[xiyX2, -> ,x r ,yi,y2, -,ys]]i which we call the tensor product of X and y.After showing several general properties of tensor products, we will prove theorems which give bounds for the number of indecomposable components in the direct decomposition of X < §> Y.