Warning: There are lots of photos and lots of thread colour changes involved in this tutorial.
Disclaimer: I'm an aussie but this I've used quilting rulers to make these drawstring bags so all of my measurements are in inches (sorry about that)! I will try to convert to centimetres as I go along.
Cut 2 pieces of fabric for the outer bag - 9.5 inches x 9.5 inches - 24.1 cm x 24.1 cm
Cut 2 pieces of fabric for the inner bag - 9.5 inches x 9.5 inches - 24.1 cm x 24.1 cm
Place right sides together (separately) for the inner and outer.
For the outer bag, sew along 3 sides using a 1/4 inch seam (0.6 cm)
For the inner bag, sew along 3 sides using a slightly larger seam allowance, but remember to leave a small opening at the bottom, and backstitch at the edges of the opening.
Outer bag - clip the bottom corners to take away the bulkiness, turn right side out and iron flat.
Make bias tape following the instructions for your bias tape maker.
I cut a strip 2 inches wide (5.1 cm) x 18 inches long (45.7 cm) and used my Clover 25 Bias Tape maker.
Turn the ends of the bias tape over and iron flat
Pin the bias tape onto the outer bag (1 inch from the top of the bag) - 2.5 cm from top.
Sew the bias tape onto the outer bag along the top edge and the bottom edge. Don't sew along the end as this is where the drawstring will thread through later.
Place the outer bag inside the inner bag - the right side of the outer bag will be facing the right side of the inner bag.
Secure the top edges together using pins or clips.
Check that the layers are even.
Topstitch along the top using a 1/4 inch seam allowance (0.6 cm)
Pull the outer bag through the small gap at the bottom of the inner bag
Stitch the gap closed at the bottom of the inner bag
Push the inner bag back inside the outer bag and topstitch very close to the edge.
It's now time to make the drawstring. You can really use anything you like for a drawstring but I'm using bias tape again.
Cut a strip 2 inches wide (5.1 cm) x 38 inches long (96.5 cm).
Make the bias tape and then fold in half (keeping the raw edges inside) and iron flat.
Stitch the bias tape closed along the outer edge and the ends.
Attach a safety pin and thread the drawstring through the open channel on the bag.
Just to ensure that the drawstring doesn't get tugged out acidentally, it's a good idea to stitch it in place on the opposite side to the channel opening.
The drawstring is now securely stitched into place
The finished product!
These can be made in many different sizes so just scale up the measurements to suit the size that you need.