Ok I might have gotten a little carried away with this... Instructions with many pictures are under the cut, it can be done by hand or on a sewing machine. Click any picture to view full size, and let me know if anything doesn’t make sense. Happy sewing!
Materials:
Fabric
Ruler or measuring tape
String or cord
Needle and thread
Iron
a safety pin
If you don't have any fabric on hand, check out the quilting section of the fabric store for small amounts of colorful cotton, look for "fabric quarters" or "fat quarters" (a quarter yard is 18 in by 18 in) or look for remnants. For the draw strings, you could probably use any kind of string or cord, ribbon, etc. I used cotton string I took from my parents, which I twisted to make it look nice (more on that later) so just use what you have or whatever looks nice with your fabric. An iron isn't strictly necessary, but ironing where you fold the fabric makes it a lot easier, and if you do iron, its small enough you can probably get away without pinning anything.
The whole bag is constructed from one rectangle of fabric, measuring 9.25 in x 3.75 in, this should get you a finished bag that's 4 in tall and 3 in wide:
[Note on size: I based this off of the 3 in x 4 in bag that came with my diva cup size 1, and it fits that cup perfectly. Closing it with the drawstrings makes the useable length of the bag a bit smaller that 4 in, so there’s not much extra space vertically. Check the size charts, and if the total length of your cup (with stem) is longer, you may want to increase the length of the bag. Just make your initial fabric piece longer and follow the rest of the given measurements. Keep in mind that because the fabric is folded, an extra inch in the original rectangle with give you an extra 1/2 inch in bag length.]
Fold your rectangle in half lengthwise, right sides of the fabric touching, and iron that crease. Turn down the top edge of the fabric so that 5/8 in of the right side of the fabric shows, iron this crease too. Turn it over and fold down the other side the same way. These turn downs will form the pockets that the draw stings go through. Note: This dark fabric I'm using doesn't have a defined right and wrong side, so I'm showing it along side the finished green bag (inside out) to give an idea of where right and wrong sides of the fabric will show:
Now sew seams up the sides from the bottom fold up to the edge of the turned down fabric, make sure you don't sew these flaps down. Seam allowance is 3/8 in, as marked in the picture:
Now time for a little origami. Unfold the top turn-downs, and fold the flaps created by the seams inward so that the right side shows. Iron them in this position:
Only now may you fold the top flap back down and iron the corners in place so that it looks like the next picture:
Only the side facing up is visible, but the side touching the table should look identical, so make sure you do this on both sides.
Now you can sew a seam from right to left across the top flap, making sure you get as close to the edge as possible to sew down those folded over edges. At those edges, the needle will punch through a total of four layers of fabric. Use a seam allowance of 1/4 in from the raw edge (which equals 3/8 in of “pocket” space above.) Then turn the thing over and do the same thing to the other flap:
Now you're done with the sewing part. Make sure all your seams are secure and nothing's going to unravel, then go ahead and turn it inside out. Boom. Push the corners out all the way with a fingernail, or something pointy, if you have to.
Give the back a quick once over with the iron so it lays flat.
Ok drawstring time. Like I said, you can use whatever you want. I was looking for thicker cotton string like the kind people use for macramé, but the stuff I ended up with was thin. So I decided to twist two strands together, which also looks nice. The twisting thing is a little finicky, and I couldn’t take pictures of doing it because I needed both hands, so if you have thicker string, or just don't want to twist, then ignore these instructions.
Twisting instructions:
The idea is to twist the string, then double it back on itself so that it twists up like an annoying phone chord when you hang up the phone.
Start out with one 25 in length of string. Pull the sting taut, and with the fingers of one hand, twist the string tighter in the direction that the strands are already twisted, until it’s difficult to twist any further. If you just put slack in the string it won’t twist up nicely from the middle, so try to hold it taught while you get both ends together (I use my teeth to help) then try to coax the folded part into twisting a little before letting it go, it will do what it wants naturally. Tie an overhand not near the end with the cut edges to keep it from unraveling, make a second one the same way, and it should look like this:
If you didn’t do the twisting thing, get two pieces of your string about 12 in long (this should give you some extra for tying knots and attaching beads or whatever at the end.) From here on it’s the same no matter what you’re using for drawstrings. Attach one end of one string to a safety pin and use that to push it all the way through one of the “pockets,” and then back in the other direction through the other pocket so that both ends of the string hang off one side of the bag.
Do the same thing with your other string so that both of it’s ends are hanging of the other side. On each side, make sure both strands are of equal length, then hold the two together and tie an overhand knot. If you want beads or something you can put those on right before you tie the knot. Do this on both sides such that when the bag is open , it’s about the same distance from the edge to each knot. How much extra there is is personal preference. For this one I didn’t leave much extra string at all, the bag can barely open and that’s it. When they’re nice and even, trim off the extra string past the knots and you’re done!
Here’s a close up of the green bag inside out for reference as well as a comparison of the size of the bag with the cup (diva size 1)
Let me know how it goes for you!