Step 1:
I used a paper of about 15x30 cm.
Fold in three parts of the same size.

Step 6:
Fold over these three prefolded lines.

Step 5:
Fold over these two lines, use the prefolded squares pattern as guidance.

Step 2:
Fold in half and unfold the model afterwards.

Step 4:
Fold in half two times and unfold the model afterwards.

Step 3:
Fold in three parts of the same size.

Step 10:
Now fold this square into a 45 degree angle. All mountain-folds are prefolded.

Step 8:
Pull / fold the left square into a 45 degree angle, see arrow on the left.
The corners indicated by the two large arrows are pulled to the left while you do this.

Step 9:
This is the square which is folded into a 45 degree angle.
Fold both edges on the left into a straight angle.

Step 7:
Fold both edges straight upwards over the prefolded lines.

Step 16:
Prefold in half over both lines.

Step 15:
The cap paper is a little bit wider than 4 prefolded squares of the bottle paper, this makes it fit nicely around the neck of the bottle.
The video shows a another way of making the cap.

Step 12:
Repeat step 10 three more times.

Step 11:
Repeat step 10 on these two places (make the same folds on the other side).

Step 14:
Done....

Step 13:
Fold over this line, make the same fold on the other side.
And glue all edges together.

Step 19:
Fold the right square on top of the left square, see arrow.

Step 20:
Repeat step 19 two more times and glue the edges together.

Step 18:
Fold the edge to the prefolded line, see purple arrow.

Step 17:
Prefold three edges to the centerlines.