Introduction: Cardboard Nautilus Costume

As a school project I created and constructed this costume using only cardboard and slotted construction. The nautilus is part of a line of marine-themed costumes my team and I designed. We designed our costumes to be Halloween costumes for middle schoolers.

My goal was to create an environmentally friendly, marine themed costume using only cardboard and slotted costruction.


The costume is:
+sized to a middle schooler
+made completely of cardboard
+easy to construct and assemble
+light weight

The costume has:
+slots in order for construction
+room for movement

The costume:
+allows for movement
+allows a child to reach a house's door bell
+fits comfortably


The costume must:
+be made of cardboard
+only use slotted costruction
+only be made using household tools
+fit the marine theme

Important Note:Instructions are based off of a LARGE (5’-5’5” person) sized costume. Adjustments will have to be made to fit other sizes.

Step 1: Gathering Matherials

Below you will find a chart with all the supplies and tools you will need to construct the costume as well as the various parts you will be making and the uses of the tools. In this section, I will also describe the circle method, which you will need to know to complete the second step in making this costume. The circle method is depicted in the third picture in the slide below. All the parts will look like the last picture in this slide.

Circle Method:
1. Draw a square with each side being the same length as the diameter of your circle.

2. Draw an “X” through the square extending from corner to corner and passing through the
exact center of the square.

3. Draw a small tick mark to mark the half of each of the four converging lines.

4. Draw tick mark to mark the half point between the half point of the line and each corner of the square.

5. Draw a small tick mark at the exact center of each side of the square.

6. Draw a circle that touches all the outer tick marks.

Step 2: Creating the Shell Sides

Part P1: Shell Sides
1. Use the large compass or circle template (T5) or the circle method (procedure stated below) and pencil (T4) to draw a circle with an 18” radius on your 3’x4’ sheet of double ply cardboard (S2). DO NOT CUT OUT!

2. Use your smaller circle template, compass (T5), or the circle method to cut out a smaller circle with a 3” radius in the exact center of the larger circle and cut out using your utility knife (T2). This is the arm hole.

3. Next, you will draw an isosceles triangle on the circle (T4). The base is 16 ¼” long and touches the edge of the large circle at its two endpoints. Make all your measurements using your ruler (T3). The third vertex of the triangle is 1 ¾” (T3) from the outer edge of the armhole.  The vertex will lie on an imaginary line at a right angle to and bisecting the baseline. The congruent sides of the triangle are 15 1/8” long. Draw the two congruent sides, AB and AC, from the endpoints of the baseline which are on the large circle to the third vertex you drew near the armhole. 

4. Extend the lower congruent side, AC, of the triangle an additional 4” outside the large circle. Draw a straight line from the new endpoint of the extended side of the triangle and extend it tangent to the large circle.  We'll call this line CD. 

5. The outline of the large shape is now the lines AB and the extended AC, the tangent line CD, and the larger arc of the outer circle between lines AB and CD. Cut out your large shape using the utility knife (T2). Keep in mind that you will cut out the triangle, and include the extended side in your final product.

6. 1 ½” in from the long edge drawn in step 4, cut a slit 2”x1/8”. Cut out four more slits with the same dimensions all 1” apart.

7. On the shorter side of the “triangle”, perpendicular to this side, and 1 ½” in from the outer edge of the large circle, cut a slit 2”x1/8”.

8. Mark a point on the large circle one foot from the point at which the shorter line of the triangle meets the circle. Make two more marks likewise along the circle at 1' intervals from each other.  At each of the three marks, cut a slit perpendicular to the circle 2" long by 1/8" wide.

9.On the straight edge of the circle, extending from the extended line in step 4, 6 ¾” from the very edge of the extended line , cut a 2”x 1/4” slit perpendicular to the outermost edge of the large circle. Cut an identical slit 6 1/8” down from the first one. Then cut one more slit 9” from the second slit.

10. Trace the finished shell side onto your second sheet of 3”x4” double ply cardboard (S2) and cut out. Line the two shell sides up and make sure that all the slots and dimensions line up exactly. You cannot afford mistakes.

Step 3: Creating the Shell Back

Part P2: Shell Back
1. Cut out a piece of cardboard (S1) to 3’x 1 1/3’ using your utility knife (T2). Cut two ¼” wide, 1” long slits on each of the long sides, one eighteen inches from the end and the other 1 ½’ from the same end.

2. On the end 18” from the first slit, mark two more slits, 3/8” wide and 2” long, perpendicular to the previous four, ¾” from the long end.

3. Cut out another piece of cardboard (S1) to 31”x16 ½” using your utility knife (T2). Cut three ¼” wide, 1” long slits on each of the long sides. The first will be 13” from the short end, the second 6 1/8” from the first, and the third 9 ¾” from the second.

4. On the end 13” from the first slit, mark two more slits, 3/8” wide and 2” long, perpendicular to the previous six, ¾” from the long end.

5. Bend (create folds in) the shell in as many places as possible to create a curve shape, but do not bend the shorter ends at the slots or it will not fit into the costume!

Step 4: Creating the Connectors

Part P3: Connectors
1. With your pencil (T4) draw on your piece of 1’x 1 ½’ double ply cardboard (S4) ten 6”x 3” rectangles.

2. Cut out the rectangles.

3. On the right side of the rectangle (when the two 3” sides make up the top and bottom), 2” from the top, create a 1”x 1/8” slit parallel to the top on each rectangle.

4. On the bottom side of each rectangle, create a 2”x 3/8” slit in the exact center, perpendicular to the top.

Step 5: Creating the Tentacles

Part P4: Tentacles
1. Draw a line to mark the halfway point, perpendicular to the long side of your 32”x 16 ½” single or double ply cardboard. Either type will work.

2.Draw four 3 ¼”x 4 ½” rectangles in the following fashion: one on the top of the half of the piece of card board, one touching the halfway line, one on the top, one on the line, and the same on the other half of the cardboard sheet.

3. Extend the long lines and make them into wavy patterns that get skinnier from the rectangle up until they reach the point. Do not make the same wavy pattern for each. Be creative! Change the wavy line pattern around each time to create interest.

4. Cut out all the tentacles.

5. Create slots on the bottom of each tentacle, opposite the wavy side, perpendicular to the bottom of the tentacle when the point faces up, that are 2”x 3/8” and in the exact center of the bottom side.

6. Bend the wavy part of the tentacle in as many places as possible to create a curve, which can be done best by rolling the wavy part around a thin, cylindrical object, or using your fingers to roll it against your leg as in the picture above.

Step 6: Personalizing the Costume

If you would like to personalize your costume with paint or marker or any other medeum, right now is the time to do it. I did not personalize my costume, so I have no pictures for this step.

Note: If you would like to paint your costume, do so on both sides, or else your costume willcurl as it dries, and you will not be able to assemble it.

Step 7: Assembling the Costume

1. Insert the slot on the short end of the longer shell back piece into the slot at the top of the shell side.

2. Curl the shell back around so that the slots align.

3. Assistance is needed now and for the rest of the assembly. Stand the costume upright with the aid of another person. Have your partner hold the shell side in place as you insert the connectors into the slots, bottom in first.

4. Have your partner hold the assembled part and slide the top slot of the other shell side into the other slot on the end of the shell back.

5. Slide the connectors into the slots on the second shell side in the same fashion as in Step 3.

6. With the help of your partner, carefully turn the second shell side of the costume upside down so that it is on the just assembled shell back.

7. Slide the short end of the smaller shell back piece into the front most slots on the extended side of the circle while your partner holds the costume upright.

8. Wrap the shell back around so that all the slots on the shell back and sides match up exactly. Slide in all the connectors in the same fashion as in Step 4. Do this on both sides and all slots. Make sure your partner has a good grip on the costume.

9. With the aid of your partner, turn the costume right side up. In the eight slots behind the slots for the shell back on the extended side of the circle, slide in your tentacles in the same manner as you would connectors. Make sure the tentacles are all facing outwards, away from the shell. Change them up a little so that one tentacle will be going off to the left and one to the right to make it more interesting.

At the end of step 9, the costume should look like the main picture.

Step 8: Trying on Your Costume

Try on your costume! In order to get inside the costume, you will have to crawl into the shell through the space between the two parts of the shell back and slide your arms through the armholes.  Enjoy!