A blintz fold takes a square and folds all four corners to its centre; a double blintz base repeats that operation on the result. Round 1's crease lines connect the midpoints of the square's edges — folding each corner triangle onto the centre leaves a smaller square, rotated 45°, at half the area. Round 2 blintz-folds that square the same way: its corners (the original edge midpoints) fold to the same centre point again, along creases exactly halfway in — producing a square with a quarter of the original area, back in the original orientation, with several layers stacked at its centre.
Every fold here is a real rigid rotation about the crease line as an axis, composed in the order the paper actually experiences it: a piece creased in round 2 rotates about its own local axis first, then is carried along by whatever round-1 rotation its parent flap is undergoing — exactly like a chain of hinges.
p' = axis_pt + R(axis_dir, θ) · (p − axis_pt)
final(p) = R1(θ1) · R2(θ2) · p_flat // round 2 nests inside round 1
- Round 1 fold — sweeps all four outer corners inward, hinging on the diamond formed by the edge midpoints.
- Round 2 fold — sweeps the resulting square's four corners in again, along creases at the quarter-points of the original sheet.
- Layer spread — a tiny visual gap between stacked layers so the crease structure at the centre stays readable; real paper has this too, from its own thickness.
- Auto-fold — plays both rounds back to back, the way you'd actually fold the paper.
Real-world relevance: the double blintz base is the starting square for many representational origami models (e.g. bases needing a fine reference grid) — it converts one crease system into a smaller, more subdivided sheet without any cuts.