Three-dimensional folding of the triangular lattice

We study the folding of the regular triangular lattice in three-dimensional embedding space, a model for the crumpling of polymerised membranes. We consider a discrete model, where folds are either planar or form the angles of a regular octahedron. These “octahedral” folding rules correspond simply to a discretisation of the 3d embedding space as a Face Centred Cubic lattice. The model is shown to be equivalent to a 96-vertex model on the triangular lattice. The folding entropy per triangle ln q3d is evaluated numerically to be q3d = 1.43(1). Various exact bounds on q3d are derived.