Step 1:
Glue two squares together or fold a large square in half.
Prefold in half over both lines.

Step 6:
Fold over this line.

Step 5:
Turn the model.

Step 2:
Fold over these two lines, the left line is already prefolded. Use the white bar as guidance, all three parts are the same length.

Step 4:
Press flat.

Step 3:
Fold the edges to the centerline.

Step 10:
Fold over these two lines. The light blue parts go below the upper paper layer.

Step 8:
Fold over this line and turn the model again.

Step 9:
Fold over the two outer lines first.

Step 7:
Press flat.

Step 16:
Curve both upper ends towards each other and press the model inwards on the places indicated by the two large arrows.

Step 15:
Fold over this line and turn the model.

Step 12:
Fold over these two lines.

Step 11:
Fold over these two lines.

Step 14:
Fold over these two lines. The light blue parts go below the upper paper layer.

Step 13:
Press flat, see arrows.