Treewidth of Cartesian Products of Highly Connected Graphs
  The following theorem is proved: For all $k$-connected graphs $G$ and $H$ each with at least $n$ vertices, the treewidth of the cartesian product of $G$ and $H$ is at least $k(n -2k+2)-1$. For $n\gg k$ this lower bound is asymptotically tight for particular graphs $G$ and $H$. This theorem generalises a well known result about the treewidth of planar grid graphs. 
David R. Wood
math.CO cs.DM