Revetted bunkers are usually constructed with stacked pieces of sod. When I visited David Bataller at the PGA Catalunya Resort, he showed me this revetted bunker. He built it using natural materials, but he didn't use turfgrass sod. The question was, just what material is this?
The correct answer is cork, given first by Dr. Brett Morris,
and then by Dave Wilber:
@asianturfgrass if in Spain, cork?— Brett Morris (@brettmorris73) December 28, 2012
@asianturfgrass it's cork. I'm late, but I knew!!— Dave Wilber (@TurfgrassZealot) December 28, 2012
Here is a closer look at this bunker.
And here is a cork tree on the course at the PGA Catalunya Resort.