Red pine, ratchet strap.
Iteration pictured is 6 Posts #4 (short inside, tall outside).
Photo Credits: Mark Prier
The 6 Posts series is a structured game. Using thirty saw cuts to create thirty-six pieces from six wooden posts, each iteration is one possible arrangement out of the unfathomable number of permutations afforded by a simple six by six grid held together with a ratchet strap.