Competitive Origami

• A. A fold where the paper is folded away from you, creating a ridge pointing toward you
• B. A fold where the paper is folded toward you, creating a crease that dips away from you ✓
• C. A fold that cuts the paper into two separate pieces
• D. A fold made by unfolding a previously creased section completely flat

Why: A valley fold brings the paper toward you so the crease forms a V-shaped valley when viewed from the front. Mountain folds are the opposite, folding away from you to form a ridge.

• A. A4 printer paper
• B. A 15 cm (6 inch) square ✓
• C. A 50 cm square
• D. Any rectangular sheet with no fixed proportions

Why: Many beginner and intermediate models are designed for square sheets, and a 15 cm (6 inch) square is a common standard for both practice and reference diagrams, making results comparable.

• A. It makes the paper heavier so the model stands up better
• B. It ensures the folds align accurately so the final model has clean lines and symmetry ✓
• C. It changes the color of the paper permanently
• D. It is only decorative and has no effect on the structure

Why: Judges evaluate accuracy, symmetry, and clean detail. Sharp, well-aligned creases are what allow the model to hold its form and match the intended design precisely.

• A. Cutting a flap off the model with scissors
• B. Opening a flap of paper and flattening it into a new shape while keeping the same base ✓
• C. Soaking the paper in water to soften it
• D. Folding the paper into thirds in a single motion

Why: A squash fold opens a layered flap and presses it flat along existing creases, transforming a section of the model into a new shape without tearing or cutting the paper.

• A. Fold the paper as quickly as possible to save time
• B. Create a reference or pre-crease pattern so folds land exactly where intended ✓
• C. Glue the layers together for stability
• D. Skip the base and begin with the decorative details

Why: Pre-creasing and establishing a crease pattern from the diagram sets accurate reference lines, which is essential for precise, repeatable results in competition-level folding.

• A. A valley fold
• B. A mountain fold ✓
• C. A cut line
• D. A reference line for measuring

Why: By the standard convention used in origami diagrams, a solid line indicates a mountain fold, meaning the crease folds away from the viewer and forms a ridge, while a dashed line indicates a valley fold.

• A. A mountain fold
• B. A valley fold ✓
• C. An unfolded flat surface
• D. A cut that must be made with scissors

Why: A dashed line represents a valley fold, where the paper folds toward the viewer and forms a trough. This is the complement of the mountain fold, which is shown as a solid line.

• A. Axial line
• B. Unassigned or undetermined crease ✓
• C. Edge line
• D. Reverse fold line

Why: Many crease patterns use a dash-dot (or similar) notation for creases whose direction is not yet fixed, often used during design to indicate a fold that will be assigned as mountain or valley later.

• A. The number of mountain folds must equal the number of valley folds only in total
• B. The angles between adjacent creases must sum to 360 degrees and the mountain and valley folds must differ by exactly two
• C. Maekawa's theorem: mountain and valley folds at any vertex must differ by exactly two ✓
• D. All creases must be the same length

Why: Maekawa's theorem states that at any interior vertex of a flat-foldable crease pattern, the number of mountain folds and valley folds differs by exactly two, so |M - V| = 2. Kawasaki's theorem separately constrains the angles.

• A. A cut that separates the paper
• B. The boundary of the paper, which is not a fold ✓
• C. A valley fold along the outer edge
• D. A line for gluing sections together

Why: The outer boundary of a crease pattern marks the edge of the square or sheet of paper. It is simply the paper's border and does not represent a fold or a cut, which is why it is drawn as a plain outline.

• A. A flat, unfolded sheet of paper with no creases
• B. A folded form with multiple flaps and points that serves as a starting shape for many models ✓
• C. The final decorative finish applied to a completed model
• D. A type of paper with a heavier weight used for structural support

Why: A base is an intermediate folded form, such as the bird base or preliminary base, from which many different models can be developed by further folding the flaps and points.

• A. A diagonal valley fold followed by a mountain fold along the midline ✓
• B. Folding all four corners to the center without any prior creases
• C. Rolling the paper into a cylinder
• D. Cutting the paper into four equal squares

Why: The preliminary base begins with creating both diagonal creases and a midline crease, then collapsing the paper into a square with four flaps, so the diagonal valley fold is a standard first step.

• A. A waterbomb base has a triangular shape with flaps folded to the same side, while a preliminary base is square with flaps folded to both sides ✓
• B. A waterbomb base uses wet paper, while a preliminary base uses dry paper
• C. A waterbomb base requires cutting, while a preliminary base does not
• D. There is no difference; the two names refer to the same form

Why: The waterbomb base collapses into a triangle with all flaps on one side, whereas the preliminary base collapses into a square with flaps split between the front and back.

• A. Crisp creases make the paper harder to tear during later folding steps and ensure the base collapses accurately ✓
• B. Crisp creases change the color of the paper permanently
• C. Precise creases are only needed for decorative purposes after the model is finished
• D. Creases reduce the total number of folds needed to complete a model

Why: Sharp, accurate creases allow the paper to collapse predictably into the intended base shape, and sloppy creases can throw off alignment and symmetry in the finished model.

• A. Reversing the paper's color from one side to the other
• B. Inverting a flap or point by folding it inside the model along an existing crease ✓
• C. Undoing all previous folds to start over from a flat sheet
• D. Cutting a flap off to shorten the model's length

Why: A reverse fold takes an existing flap or point and pushes it inside the model between its layers, reversing its direction to create new shapes such as beaks, tails, or legs.

• A. To make the paper waterproof
• B. To soften the paper fibers so creases can be shaped into curves and rounded forms
• C. To dye the paper a darker color
• D. To make the paper stronger and more rigid

• A. Glossy photo paper
• B. Thin copy paper
• C. Thick, absorbent paper such as Japanese washi or kraft paper
• D. Laminated cardstock

• A. Folding all the creases dry and then spraying the model with water
• B. Lightly dampening the paper with a brush or sponge and allowing it to absorb moisture
• C. Submerging the paper completely in water for several hours
• D. Heating the paper with a hair dryer until it becomes pliable

• A. To prevent the paper from tearing when it is unfolded
• B. To make the model turn a different color
• C. To lock the shaped curves in place so the model keeps its form
• D. To remove the ink from printed paper

• A. The paper becomes slightly translucent
• B. The paper begins to tear or pill at the surface and loses its structure
• C. The paper smells faintly of cedar
• D. The paper becomes easier to fold with sharp creases

• A. A single folded piece that is assembled with other identical pieces to form a larger structure ✓
• B. A single uncut sheet of paper folded into a complete three-dimensional model
• C. A tool used to crease paper precisely along straight lines
• D. A type of paper with a special texture that prevents tearing during folding

Why: A module is one folded unit, usually made from a square of paper, that is repeated many times and interlocked with other identical units to build a larger polyhedron or pattern.

• A. Equilateral triangle
• B. Regular pentagon
• C. Square ✓
• D. Circle

Why: Most modular units are folded from squares because squares divide neatly into halves and quarters, making the precise, repeatable creases needed for consistent modules.

• A. A pattern made by repeating a shape so that it covers a surface with no gaps or overlaps ✓
• B. A folding technique that requires cutting the paper into many small pieces
• C. A flat model with only one crease running through its center
• D. A structure held together with glue rather than interlocking folds

Why: A tessellation is a repeating tiling pattern that covers a plane completely without gaps or overlaps. In origami, tessellations are created by repeating a folding pattern across a sheet of paper.

• A. They are folded from specially treated paper that sticks to itself
• B. Their pockets and tabs fit tightly into one another, creating friction that locks the structure ✓
• C. They are stapled at the corners during the final assembly step
• D. They are wrapped in tape to prevent them from separating

Why: Each unit has flaps (tabs) and pockets (slots). When tabs are inserted into pockets, the friction and tension of the folded paper keep the pieces locked together.

• A. Icosidodecahedron ✓
• B. Tetrahedron
• C. Cube
• D. Octahedron

Why: The icosidodecahedron is commonly built from 30 identical units, with each unit contributing to a vertex or edge arrangement that forms the full 30-faced solid. Its structure makes it a classic beginner-to-intermediate modular project.

• A. It shows the finished model in full color
• B. It maps every fold line so the design can be reproduced and checked ✓
• C. It lists the paper brand and weight needed
• D. It describes the history of the folding technique

Why: A crease pattern is a diagram of all the mountain and valley folds on an unfolded sheet. It is the blueprint that lets designers record, test, and share a model.

• A. A cut line
• B. A mountain fold
• C. A valley fold ✓
• D. An edge of the paper

Why: Standard crease pattern notation uses solid lines for mountain folds and dashed lines for valley folds, so a dashed line indicates a valley fold.

• A. Squares are cheaper to produce than other shapes
• B. Squares can be divided into equal grid sections, making precise folds easier to plan ✓
• C. Squares always produce animals automatically
• D. Squares cannot be folded in half

Why: A square's symmetry and right angles allow for precise divisions such as halves, quarters, and diagonals, which form the foundation for most folding systems.

• A. Sketching the target subject and identifying its major parts, such as legs, wings, or a head ✓
• B. Buying specialized glue
• C. Cutting the paper into strips
• D. Folding the paper as small as possible

Why: Beginning designers break the subject into its key components and proportions, then plan how each part can be formed from flaps of paper.

• A. Measuring the paper's thickness with a ruler
• B. Folding the model repeatedly from the crease pattern to check that it works and can be reproduced ✓
• C. Displaying the model in a museum
• D. Sending the design to a paper manufacturer

Why: Testing means folding the design from start to finish, checking that each step is possible, that the final shape matches the intent, and that others can follow the instructions.

• A. The number of colors used in the paper
• B. Crisp, well-defined creases and clean, accurate folds ✓
• C. The total time spent on the model during the round
• D. The size of the finished model compared to the paper

Why: Judges reward crisp, well-defined creases and clean, accurate folds because precision demonstrates technical skill. Colors, time, and relative size are not core judging criteria in most competitions.

• A. Judges require two models to be submitted for every entry
• B. To protect against tearing, creasing errors, or a fold that cannot be corrected ✓
• C. To use as a template for folding the main model
• D. Backup paper is needed to fill the required display time

Why: Paper can tear or develop irreversible errors during folding, so a backup sheet lets a competitor restart without losing the entire round.

• A. Memorizing the diagram without ever practicing the fold
• B. Practicing the complete folding sequence repeatedly while timing yourself ✓
• C. Folding the model only once the day before the event
• D. Skipping the difficult steps so the model finishes faster

Why: Repeated timed practice builds muscle memory and reveals which steps are slow or error-prone, so the competitor can improve both speed and accuracy.

• A. The model is folded from paper that is too thin
• B. The model has visible wrinkles, smudges, or uneven surfaces from careless handling ✓
• C. The model uses a traditional base rather than an original design
• D. The competitor folded the model with their non-dominant hand

Why: Visible wrinkles, smudges, and uneven surfaces indicate careless handling and detract from the finished appearance that judges evaluate.

• A. That the paper matches the specific size and type required by the rules for that category ✓
• B. That the judges have seen their previous competition results
• C. That no other competitor is folding the same model
• D. That the model can be folded in under one minute

Why: Each category has specific paper requirements, and using the wrong size or type can lead to disqualification regardless of folding skill.