Step 1:
I taped aluminium foil to the backside of this paper. The size is 30x40 centimeters
(2 standard printer/copy papers glued together over the length).
Fold in half over the red line.

Step 6:
Fold over these 3 lines.

Step 5:
Fold the edges to the centerline.
Then unfold the folds of step 4 and 5

Step 2:
Valley-fold over this line.

Step 4:
Fold both edges to the centerline.

Step 3:
Prefold in half

Step 10:
Fold over this red line

Step 8:
Prefold both edges to the centerline.

Step 9:
Mountain-fold over the 2 lines in the middle and valley-fold over the 2 outer lines.

Step 7:
Prefold in half

Step 16:
Fold over these 3 lines

Step 15:
Fold into a tube over the prefolded lines, use tape or glue

Step 12:
Repeat step 10 and 11 on the other side.

Step 11:
Press flat, see arrows.

Step 14:
Fold the flap to the right

Step 13:
Mountain-fold over this line

Step 21:
Fold both edges straight upwards.

Step 19:
Fold the flap to the left, see step 21 for the result.

Step 20:
Prefold over this line.

Step 18:
Mountain-fold over this short red line

Step 17:
Press this edge flat, do the same on the other side.

Step 22:
Press/fold the edge inwards, do the same on the other side

Step 25:
Press/fold the edge inwards

Step 26:
This is a more detailed picture of the result

Step 24:
Tape/glue the edges together

Step 23:
Fold both inner edges upwards.

Step 27:
Fold the edge on the left over the edge on the right. Do the same on the other side.

Step 28:
Use tape or glue to connect both parts.