How To Make A Paper Bridge | The Fold That Beats Flat

You probably picture a paper bridge as a flimsy sheet sagging between two books, collapsing at the first sign of a penny. That flat-sheet design is indeed weak—almost useless for holding anything. But the same sheet of paper, folded a certain way, can surprise you.

The trick isn’t exotic materials or glue. It’s a simple folding technique that transforms paper from a limp surface into a load-bearing structure. Here is how to make a paper bridge strong enough to hold coins, and why the shape matters more than you think.

Why A Flat Sheet Fails And A Folded Sheet Works

A flat sheet of paper laid across a gap has almost no resistance to bending. Place a single penny in the center, and the paper buckles immediately. That’s because a flat sheet handles weight by bending at the middle, with no structure to transfer the load sideways.

Folding the paper into an accordion (pleated) shape changes everything. The parallel ridges and valleys act like a truss system, distributing the load more evenly across the entire span. Science Buddies, a well-established STEM resource, calls this the accordion fold strength mechanism—a simple geometric change that dramatically increases load capacity.

The folds create vertical walls that resist compression at the top and tension at the bottom, mimicking how real steel bridges distribute forces. A flat sheet might hold zero pennies; a well-folded accordion bridge can hold twenty or more.

What About Card Stock vs. Copy Paper?

Using thicker paper like card stock instead of standard copy paper produces a stiffer, stronger bridge. The stiffer material resists bending before you even fold it, giving the accordion ridges more rigidity. For a basic experiment, copy paper works fine—just fold it carefully.

But the real lesson is that shape, not material thickness, does most of the work. A copy-paper accordion bridge easily outperforms a flat card-stock bridge every time.

Why The Geometry Trick Feels Counterintuitive

Most people assume that adding material—more layers, tape, or thicker paper—is the only way to make paper stronger. That instinct comes from everyday experience: thicker cardboard holds more weight than a business card. But engineering doesn’t always work that way.

The accordion fold works because it converts the paper from a two-dimensional surface into a three-dimensional structure. Those ridges and valleys are essentially tiny trusses, and trusses are one of the most efficient shapes for carrying loads over a gap.

You can see this principle in real bridges. Steel truss bridges, arch bridges, and even some modern origami-inspired designs use geometry to distribute weight. The paper bridge is just a miniature version of the same logic.

Here are the key reasons a folded bridge works better than a flat one:

• Load distribution: The accordion folds spread the force from the center toward the supports, reducing the peak stress at any single point.
• Vertical walls resist bending: Each ridge acts like a tiny I-beam, with the paper’s fibers aligned to resist downward force.
• Arch action in the folds: The curved peaks of the accordion create small arch shapes, which transfer weight outward and downward along the curve.
• No glue needed: The folds themselves hold the shape; you don’t need adhesive to get a strong bridge from a single sheet.
• Same material, different result: A folded bridge uses exactly the same amount of paper as a flat sheet, yet performs orders of magnitude better.

Once you understand why geometry wins over bulk, the design becomes obvious: fold first, test second, and never trust a flat sheet.

Step-by-Step: How To Make A Paper Bridge That Holds Pennies

This is the classic paper bridge challenge used in classrooms and STEM programs. You need one sheet of standard 8.5 x 11 inch copy paper, two stacks of books or blocks of equal height, and a handful of pennies or other small weights.

Set your supports (books, blocks, or cups) about 6 to 8 inches apart. A standard distance used in many experiments, including PBS’s bridge activity, is 20 cm (about 8 inches) between supports. The gap should be just under the length of your paper sheet.

These numbers are approximate and depend on fold precision, paper quality, and exact support spacing. The key takeaway: any folded design dramatically outperforms a flat sheet, and folding paper more tightly generally yields a stronger bridge.

Folding The Accordion Bridge

Lay the paper flat. Fold one short edge over by about half an inch (1 cm), crease it sharply, then flip the paper and fold the next section in the opposite direction. Continue alternating folds along the entire length of the paper until you have a pleated strip. The folds should run perpendicular to the gap when you place the paper across the supports.

Place the folded paper on top of your supports. The ridges should point upward, and the valleys should rest on the supports. Make sure the paper overhangs both supports by at least half an inch so it doesn’t slip off. Then start adding pennies one at a time in the center of the span.

University of Michigan researchers have demonstrated that origami-based folding techniques can create load-bearing modules for real, full-scale structures and bridges—this origami load-bearing structures research proves the principle scales far beyond paper and pennies.

Testing Your Bridge Without Breaking It Too Fast

Start with a single penny placed gently in the center of the bridge. If the bridge holds, add another penny. Continue adding pennies one at a time, placing each one as close to the center as possible. Watch for early signs of collapse: the paper may start to bow, the folds may begin to flatten, or the bridge may twist sideways.

Here are the steps to a controlled test:

1. Set up supports at 6 to 8 inches apart — use books, blocks, or sturdy cups of equal height. The span must be clear underneath.
2. Fold your paper into tight accordion pleats — about every half inch. The more folds, the stronger the bridge, but the paper gets stiffer and harder to place.
3. Place the folded bridge across the supports — ridges up, overhang on each side, and center it over the gap.
4. Add pennies one at a time — keep them in the center or stack them gently. Don’t drop them; that adds impact force.
5. Record the number of pennies when it collapses — the last penny that was successfully held before failure is your bridge’s load capacity.

If the bridge collapses after very few pennies, inspect the failure point. Did the paper tear at a fold? Did it slide off a support? Adjust your design: make folds tighter, widen the overhang, or try card stock for a stiffer structure.

Beyond The Basic Accordion: Arch And Origami Designs

An arch-shaped paper bridge is stronger than a flat one because the arch transfers the weight outward and downward along the curve to the supports. To build an arch bridge, fold a sheet of paper lengthwise into a gentle curve, then tape or hold the ends to the supports. It’s less efficient than the accordion for holding many pennies, but it teaches a different engineering principle.

The most advanced paper bridge design for a single sheet is the origami-based truss, where you fold the paper into interlocking triangular modules. University of Michigan researchers have shown these origami modules can create structures strong enough for real-world bridges and shelters. For a classroom or home project, though, the accordion fold is the fastest path to a strong result.

PBS offers a complete guide for testing bridge with pennies that walks through the setup, folding, and testing process step by step. It’s a reliable resource for parents and teachers running the activity.

The Bottom Line

The quickest way to make a paper bridge that holds weight is to fold a single sheet into tight, parallel accordion pleats and place it across two supports 6 to 8 inches apart. The folds convert the paper from a weak flat surface into a truss system that distributes load, and with careful folding, the bridge can hold dozens of pennies before collapsing.

For a classroom challenge, home science experiment, or just a fun project with kids, this method teaches real structural engineering without glue, tape, or special materials. If your first bridge fails early, tighten the folds or switch to card stock—small adjustments in geometry produce big differences in strength.