R numbers- All projects are catalogued in one of two systems, the R numbers and the T numbers. R numbers (Rule-based numbers) run from R0 to R10, with subgroups added as decimal places. This numbering system was first defined in 1998. Numbers are assigned to forms based on material used:

R0: imaginable shapes
R1: paper, cut and/or folded
R2: paper bound with string or wood
R3: with the addition of glue
R4: with the addition of a wood or cardboard armature
R5: paper pulp (paper blended in a blender and dried)
R6: paper pulp with the addition of glue and cardboard armature
R7: with the addition of a wooden base, and metal strips
R8: forms combining two or more other forms
R9: paper or paper pulp forms incorporating any other materials
R10: forms made of other materials, with no or little paper

R numbers are assigned as new forms are defined. These forms are also assigned a place in the R-number cladograms. These cladograms resemble cladograms from Biology such as Templeton’s nested clades. Where Biology make a distinction based on speciation, R numbers are arranged based on divergence of steps taken in the process of making the pieces. In 2007 the category R0 had to be added to organize the initial shape of paper used to make the forms. Pieces assigned an R0 number don’t exist, they are the idea of the shape only.

Around 2003 the R numbering system was replaced by and large with the T numbering system for a couple reasons: the variety of materials involved made the R numbers less meaningful, content became more important than form, and metaphorical systems were replaced with actual systems. However, current pieces which lend themselves to the R numbering system (such as R9.5) are still assigned R numbers rather than T numbers.