     For a project in my high school technology class, I was assigned to design and create a marine-themed line of costumes in a group. The trick is, the only material we were allowed to use was cardboard.
      My team had decided to design and create a line of marine-themed costumes for middle school children to use during Halloween or some other costumed function such as a Halloween party or a school play. We used only recycled cardboard in order to make our costumes "green" and inexpensive for the user. The theme for our marine costumes was reef animals, which include clownfish, manta rays, seahorses, sea turtles, and jellyfish. This instructable is specifically for a seahorse costume.

Specifications:
     - Must be made of recycled cardboard
     - Must be slotted construction
     - Must be suitable for middle schoolers
     - Must be marine-themed
Limitations:
     - Recycled cardboard
     - Slotted construction
     - Flat-pack design

Step 1: Gather Materials

Supply List:

S1 --- CARDBOARD.............Whole Costume
You will need two 3 1/2 by 1 foot pieces, two 1 foot squares, and two 1 1/2 foot by 3 inch pieces.

Tool and Equipment List:

T1 --- CUTTING MAT.............Cut out cardboard pieces on
T2 --- UTILITY KNIFE............Cut out cardboard pieces
T3 --- RULER.........................Measure
T4 --- PENCIL........................Drew out cardboard pieces before cutting them

Tip: Be extremely careful when using the utility knife. Only an adult should be handling the utility knife.

Step 2: Body

1. Start by measuring a 3 1/2 by 1 foot rectangle out of the cardboard (S1) using a ruler (T3).
2. Sketch the body shape shown below on the rectangle with a pencil (T4).
*Shape does not have to be exact.*
3. Cut out the shape with a utility knife (T2) over the cutting mat (T1).
4. Trace the cut-out shape with a pencil (T4) on the cardboard (S1).
5. Repeat step #3.

Step 3: Body Slits

1. Make a horizontal slit about 1 inch from the top of the body and about 1 inch from the right side of the costume with the utility knife (T2). Make the slit about 1 1/2 inches long and only wide enough for a single piece of one-ply cardboard to fit into the slit. Use a ruler (T3).

2. Make a vertical slit the same length and width as the previous slits about 3 inches from the curve of the belly. Use a ruler (T3).

Tip: See the picture below for a better understanding of the placement of the slits.

You now have the body of your seahorse!

Step 4: Fins

1. Measure a 7 inch by 6 inch rectangle out of cardboard (S1) with a ruler (T3).
2. Sketch the shape of the fin on the rectangle using a pencil (T4).
*Again, the shape of the fins does not have to be exact. If you have a better design for the fins, then use your own design!*
3. With the cutting mat (T1) underneath, cut out the shape of the fin using the utility knife (T2).
4. Trace the cut-out shape onto another piece of cardboard (S1) with a pencil (T4).
5. Repeat step #3.

The key to these fins is the end on the left side of the picture below. As you can see, the portion on the very left is wider than the rest of the "stem" of the fin. This feature ensures that the fins do not fall off of the body and will be used for the shoulder straps in the next step.

You now have 2 identical seahorse fins!

Step 5: Shoulder Straps

1. Measure a 1 1/2 foot by 2 1/2 inch rectangle on the cardboard (S1) using the ruler (T3).
2. Cut out the rectangle with the utility knife (T2).
3. Out of the rectangle, cut out the shape shown below with the utility knife (T2). A half inch (1/2") from each side should be taken off. Mark these measurements with a pencil (T4).
4. Repeat steps #1-3.

Now you have finished making the pieces for your seahorse costume!
You will now proceed to constructing the costume.

Note: If you have intentions to paint this costume, each part of the costume should be painted individually, and not once the costume is constructed. Also, be aware that paint may cause the cardboard to warp. To prevent this, paint both sides of the piece.

Step 6:

Part List:

ITEM -------- QTY --------- PART NAME
P1 ------------- 2 ------------- BODY
P2 ------------- 2 ------------- FINS
P3 ------------- 2 ------------- SHOULDER STRAPS

Below is an exploded view of all the parts and a layout of the parts.

The steps for assembling these parts will be present in the following slides.

Step 7: Fin Construction

1. Fold the two ends of the fins (P2) inwards and insert the tab into the vertical slit in the body (P1) near the belly.

2. Unfold the ends of the fin (P2) once the tab is fully inserted into the vertical slit. Repeat steps #1 and #2 on the other body piece (P1).

*Use the pictures below as a guide*

Step 8: Shoulder Strap Construction

1. Take the shoulder strap (P3) and fold the end of the tab like you did with the fin.
2. Insert the tab into the left horizontal slit near the top of the body (P1).
3. Take the other end of the same shoulder strap (P3) and repeat step #1.
4. Insert that tab into the left horizonal slit near the top of the other body (P1).
Tip: The "left slit" goes for both of the body pieces (P1) if they are facing the same way.
5. Repeat steps #1-4 with the second shoulder strap (P3).

*Use the pictures below as a guide*

Step 9: Putting the Costume On

To put the costume on, put your head in between the two shoulder straps (P3) and let the straps rest on your shoulders.

You are now ready to become the one of the most amazing marine animals - the seahorse!

Introduction: Silly Seahorse Costume