Use lightweight fabric that is the same on both sides, such as paper lame or crystal organza.
Can be all one colour, or made of sections of different colours.
Cut the fabric for the streamer approximately 9 inches (23cm) wide. The length needs to be about 3 yards (2.7m), which can be one piece or done in sections. Use a selvedge for the top end if possible, it gives a much neater finish.
Join the sections together neatly and securely :-
machine the wrong sides together, press seam open, trim one side of the seam allowance, and fold the other side round it. Machine on right side close to fold.
Optional - taper the bottom end of the streamer into a point.
Neaten all the raw edges of the streamer by overlocking/serging, or double turned hem.
Top of the streamer
Cut an oblong piece of interfacing - the width is the measurement between the 2 side seams (less bulk and neater if you don't put it over the seams). The length required is half the finished width of the streamer plus half an inch (1cm).
With top edges aligned iron or tack the interfacing to the wrong side of the streamer.
Fold the top of the streamer in half lengthways to mark a centre line down the length of the interfacing. Use a non permanent method of marking, especially if you have sheer fabric.
Fold the top corners down over the interfacing. Pin the top edge close to the centre line, on both sides, to create a triangular point at the top of the streamer. Pin and tack into place.
Cut a piece of boning the width of the streamer. Stitch it across the streamer on the wrong side at the base of the triangle, covering the folded in side edges. Sew it so that the top of the tape on the boning encloses the edge of the folded in side seams.
If you have a type of boning that you can't machine directly on to fabric you will need to make a casing across the width of the streamer to put the boning in. You could use spare fabric, bias binding, seam binding or ribbon for this. No bias stretch is needed because the casing is straight. The depth of the casing needs to be just bigger than the boning. The top edge of the casing needs to enclose the folded in side seams as above.
Put an eyelet into the top point, and use a split ring to join to a baton.