There are two kinds of people in this world: people who throw away empty paper towel rolls, and people who look at one and think, “Ah yes, future optical instrument.” Today, congratulationsyou are joining the second group. Learning how to make a periscope with a paper towel roll is one of those wonderfully simple STEM projects that looks like a craft, behaves like a science experiment, and gives everyone in the room the sudden urge to whisper, “Agent mode activated.”
A homemade periscope lets you see over, under, or around an object without moving your head into the direct line of sight. It works because two mirrors redirect light through a tube. That sounds fancy, but the build is refreshingly low-tech: a cardboard tube, two small mirrors, tape, scissors, and a little patience. No submarine required. No lab coat required. Though if you own a lab coat, this is absolutely the moment to wear it dramatically.
This guide walks you through the materials, the science, the step-by-step build, troubleshooting tips, learning ideas, and real-life project experiences so your paper towel roll periscope actually worksnot just “looks like it might work if the planets align.”
What Is a Periscope?
A periscope is a viewing device that uses mirrors or prisms to help you see from a different position. The classic example is a submarine periscope, which allows someone inside the submarine to see above the water. Periscopes have also been used in vehicles, observation tools, and educational demonstrations because they show a basic but powerful idea: light can be redirected.
For a simple DIY periscope, two flat mirrors are placed inside a tube at matching 45-degree angles. Light enters through the upper opening, strikes the top mirror, travels down the tube, hits the bottom mirror, and finally reaches your eye. In plain English: light takes the scenic route, and you get to peek around obstacles like a very polite spy.
Why Use a Paper Towel Roll?
A paper towel roll is nearly perfect for this project because it is lightweight, easy to cut, and already shaped like a tube. It gives the light a clear path while keeping the mirrors aligned. It is also free if you have recently cleaned a kitchen counter, wiped up a juice spill, or survived a spaghetti night.
The round shape does make mirror placement slightly trickier than a square box, but that is part of the fun. A paper towel roll periscope teaches practical problem-solving: how to measure angles, secure delicate parts, block extra light, and adjust the image until it looks right.
Materials You Will Need
- 1 empty paper towel roll
- 2 small flat mirrors, ideally about 2 inches wide
- Scissors or a craft knife
- Clear tape or masking tape
- Ruler
- Pencil or marker
- Cardboard scraps, optional but helpful
- Black construction paper, optional for reducing glare
- Decorating supplies, optional but excellent for dramatic flair
A Quick Safety Note
If a craft knife or razor blade is used, an adult should handle the cutting. Cardboard tubes are easy to slice unevenly, and fingers are inconvenient things to repair. If children are doing this project, let them measure, mark, tape, test, decorate, and explain the science while an adult manages sharp tools.
How the Science Works
The key idea behind a periscope is the law of reflection. When light hits a smooth mirror, it bounces away at the same angle it arrived. If light hits a mirror at a 45-degree angle, it reflects away at a 45-degree angle. In a periscope, that first reflection sends the light downward through the tube. The second mirror reflects the light again so it travels into your eye.
This is why mirror angle matters so much. If the mirrors are too flat or too steep, you may only see the inside wall of the paper towel roll, which is not exactly thrilling unless you are doing a documentary about cardboard. When both mirrors are angled correctly and facing each other, the image travels neatly through the tube.
Step-by-Step Instructions
Step 1: Prepare the Paper Towel Roll
Start with a clean, dry paper towel roll. If the roll is bent, gently reshape it. A slightly squashed tube can still work, but the mirrors are easier to align when the roll is round and stable.
If you want a sturdier periscope, wrap the tube with construction paper or thin cardstock before cutting. This helps prevent the cardboard from tearing. It also makes the final project look less like recycling day and more like a brilliant engineering prototype.
Step 2: Mark the Viewing Openings
Hold the paper towel roll vertically. Near the bottom of the tube, draw a small rectangular viewing window on the side. This is where you will look into the periscope. A good size is about 1 inch tall and 1.5 inches wide, but you can adjust it based on your mirror size.
Now rotate the tube so the top opening will face the opposite direction from the bottom viewing window. Near the top of the roll, draw another window on the opposite side. This upper window is where light will enter.
The windows should not be directly above each other on the same side. They should face opposite directions, allowing the periscope to look one way while your eye looks from the other end.
Step 3: Cut the Windows
Carefully cut out both windows. If using scissors, pinch the cardboard slightly and make a small starter cut. If using a craft knife, place the tube on a safe cutting surface and let an adult do the work.
Try to keep the edges neat, but do not panic if they look a little rough. This is a homemade periscope, not a museum sculpture. A bit of tape can clean up the edges later.
Step 4: Create the Mirror Slots
At the top window, you need the first mirror to sit inside the tube at a 45-degree angle, facing downward. At the bottom window, the second mirror should sit at a matching 45-degree angle, facing upward. Together, they should face each other inside the tube.
Use your ruler to draw a diagonal line near each window. Each diagonal should be long enough to support one mirror edge. If your mirror is square, the diagonal slot should match the width of the mirror. Cut carefully along each diagonal line to create a slot where the mirror can slide in.
If cutting slots in a round tube feels awkward, you can use cardboard supports instead. Tape each mirror to a small cardboard triangle, then tape the triangle inside the tube at about 45 degrees. This method is often easier for younger builders and anyone who has ever looked at a diagonal cut and thought, “Absolutely not.”
Step 5: Insert the Mirrors
Slide the first mirror into the top slot with the reflective side facing the upper window and angled toward the inside of the tube. Then insert the second mirror near the bottom window with the reflective side facing upward toward the first mirror.
Before taping everything permanently, test the view. Look through the bottom window. Point the top window toward a bright object, such as a wall, a window, or a colorful poster. You should see the object reflected through the tube.
If you only see cardboard, the mirrors are not aligned yet. Adjust one mirror at a time. Small changes make a big difference. A periscope is basically a cardboard tube that teaches humility.
Step 6: Tape the Mirrors Securely
Once the view looks good, tape the mirrors in place. Use enough tape to prevent wobbling, but avoid covering the reflective surface. If the mirrors shift even a little, the image may tilt, vanish, or turn into a confusing blur.
For extra stability, tape around the outside of the tube where the mirror slots were cut. You can also add cardboard braces behind the mirrors to hold the angle steady.
Step 7: Reduce Glare and Improve the Image
If the image looks washed out, line the inside of the tube with black construction paper before securing the mirrors. Dark interior surfaces reduce stray reflections and make the viewed image easier to see. This is especially useful if you are testing the periscope near bright lamps or sunny windows.
You can also add short paper “hoods” around the viewing windows. These block extra side light and make the image clearer. Think of them as tiny cardboard sunglasses for your periscope.
Step 8: Decorate and Test
Now comes the highly scientific process of making it look cool. Cover the tube with colored paper, stickers, markers, or labels. You can turn it into a submarine scope, a jungle explorer tool, a space rover viewer, or a secret hallway observation device. Keep decorations away from the windows and mirrors.
Test your periscope by looking over the edge of a table, around a doorway, or above a stack of books. Try rotating it sideways to see around corners. The more you test it, the more you will understand how mirror direction changes the view.
Troubleshooting: Why Is My Periscope Not Working?
The Image Is Missing
The mirrors are probably not facing each other correctly. Look into the tube from one end and check whether the reflective surfaces are aligned. The top mirror should send light down the tube, and the bottom mirror should send that light toward your eye.
The Image Looks Tilted
One mirror may be crooked. Adjust the mirror slowly until the image straightens. A tiny cardboard wedge behind the mirror can help hold the angle.
The View Is Too Dark
Use the periscope in a brighter area or point the top window toward something well lit. You can also make the windows slightly larger or use larger mirrors. Bigger mirrors usually capture more light and provide a wider view.
The Tube Keeps Bending
Reinforce the paper towel roll with cardstock, construction paper, or tape. If the tube collapses, the mirror angle changes, and your periscope becomes a sad cardboard telescope with trust issues.
Fun Learning Ideas
Once the basic periscope works, turn it into a mini science investigation. Ask questions, make predictions, and test changes one at a time. What happens if the mirrors are moved closer together? What if the tube is longer? What if you use shiny foil instead of a mirror? What if the mirrors are not exactly 45 degrees?
These simple experiments help explain reflection, angles, light paths, image brightness, and design trade-offs. A longer periscope may let you see higher, but the image can become smaller or dimmer. A tiny mirror may fit easily, but it may not capture enough light. Engineering is often a game of “this works, but what did it cost?” In this case, the cost is usually tape.
Best Uses for a Paper Towel Roll Periscope
- Classroom STEM demonstrations about reflection
- Homeschool science projects
- Rainy-day crafts
- Science fair demonstrations
- Optics lessons for elementary and middle school students
- Creative spy-themed games
- Hands-on engineering challenges
This project works especially well because the results are immediate. You build, test, adjust, and see the science in action. There is no waiting overnight, no batteries, no complicated software, and no mysterious missing charger. Just light, mirrors, cardboard, and the satisfying moment when the image finally appears.
Common Mistakes to Avoid
The biggest mistake is placing the mirrors in the same direction instead of facing each other. Remember: the top mirror catches the view and sends it downward; the bottom mirror catches that light and sends it into your eye.
The second mistake is using dull reflective materials. Aluminum foil may reflect light, but it usually creates a blurry image because its surface is not as smooth as a mirror. For the clearest homemade periscope, use real flat mirrors or high-quality acrylic mirrors.
The third mistake is taping too early. Always test before locking the mirrors into place. Tape is wonderful, but it is also very confident. Once it grabs the cardboard, it may bring half the tube with it if you change your mind.
Experience Notes: What This Project Teaches in Real Life
The first time you make a periscope with a paper towel roll, the project may look almost too easy. Two mirrors, one tube, a few cutsdone, right? Then reality enters the room wearing safety goggles. The mirror slips. The viewing window is slightly too small. The image shows the ceiling instead of the target. Someone says, “I think it’s broken,” even though it has no moving parts. This is the good part.
In real hands-on learning, the best moment is often not when the project works perfectly. It is when the builder realizes why it does not work yet. A child may look through the bottom window, see only darkness, and discover that the top mirror is facing the wrong way. Another builder may see a tilted image and learn that angle matters. Someone else may notice that the periscope works better near a bright window than in a dim hallway. Suddenly, reflection is not just a vocabulary word. It is a thing they can adjust with their fingers.
This activity is also a surprisingly good teamwork project. One person can hold the tube, another can adjust the mirror, and a third can announce whether the image is improving or getting worse. This usually leads to a lot of dramatic commentary, such as “Stop! I can see the lamp!” or “No, wait, now I can see your shoe.” It is funny, but it is also observation, communication, and engineering practice.
Another useful experience is learning that materials matter. A strong cardboard tube holds the mirrors better than a soft, crushed one. Clear tape may look neat, but masking tape is often easier to reposition. A larger mirror gives a better view, but it may be harder to fit inside the tube. These small discoveries teach practical design thinking: every choice changes the final result.
The project also gives adults a chance to step back. It is tempting to fix everything immediately, especially when the mirrors are crooked and the tube looks like it lost a wrestling match with a backpack. But letting kids test, fail gently, and improve the design makes the lesson stick. The finished periscope is fun, but the process is the real prize.
By the end, the builder has not just made a craft. They have created a working optical device from everyday materials. They have seen how light travels, how mirrors redirect an image, and how a simple tool can extend human vision. That is a pretty impressive achievement for something that started life holding paper towels.
Conclusion
Making a periscope with a paper towel roll is a simple, affordable, and memorable way to explore the science of reflection. With two small mirrors placed at 45-degree angles, a cardboard tube becomes a working optical tool that can see over obstacles and around corners. The project is easy enough for beginners, flexible enough for classroom experiments, and entertaining enough to make adults quietly test it when nobody is looking.
The best part is that this DIY periscope turns ordinary materials into a real science lesson. It shows that physics is not trapped in textbooks; sometimes it is hiding in the recycling bin, waiting for tape.
