For this Instructable, I made three different sized heating pads from a matching set of towels (1 hand towel and 2 fingertip towels). I used rice and a different scented sachet for each (lavender, vanilla and jasmine). The covers I made from fleece.
Step 1: Supplies
1 hand towel (16" x 28")
2 fingertip towels (12" x 18")
3 scented sachets (I bought mine from Jo-Ann Fabrics, but dried herbs would probably be better)
2 5-pound bags of rice (I didn't measure, but I think I only used about half of one bag)
Mixing bowl (large enough to handle 5 pounds of rice)
3 large Ziploc bags
For the covers:
3 pieces of fleece or whatever cozy fabric you want (I didn't measure them out ... just placed the completed bags on top of the fleece and cut large enough pieces to make a pocket and fold over the open end for each heating pad.)
Step 2: Make the Sacks
Next is to create the tubing effect that evenly distributes the contents. To do this divide up the length or width into even spacing between 2" - 3". Pin these division lines but leave 1 1/2" - 2" space at the bottom and top of these lines. Sew these lines (remember to not sew all the way up to the top or down to the bottom so that you can fill your sacks).
Step 3: Add the Filling
I'm sure using a plastic funnel would have been a lot easier than what I did next, but I worked with what I had handy and made a Ziploc bag funnel. Pour the rice mix into one of the large Ziploc bags and close it. Turn the bag upside down and cut one of the corners so that you have 1" - 1 1/2" opening. Funnel your rice mix into the opening of the largest sack (I recommend over the mixing bowl to limit clean up), stopping every once in awhile to shake the rice mix in the sack to get all of the tubes filled. This sack took the entire 5-pound bag of rice and filled it perfectly.
Follow the same procedure for the other two sacks with a lot less rice. I divided the 5-pound bag of rice in half and ended up with a lot of rice mix left over. You probably could use just 1/4 of the 5-pound bag for each sack.
Step 4: Finish the Heating Pad
The next part is optional but recommended, as you want to keep your heating pad clean.
Step 5: Make the Heating Pad Cover
Fold over 1/2", pin and sew the side that will be the opening (the opposing side will be the flap) so that the wrong side of the fabric is facing itself. Place the fabric wrong side down on your work surface, and place the heating pad on top of it, matching heating pad edge to sewn edge of fleece with even space on either side of the heating pad. Fold the fleece over the heating pad and pin the two sides adjacent to the sewn edge. Fold and pin the flap edges in 1/2" with the wrong side of the fleece facing itself. Remove the heating pad and sew the pinned edges. Turn the cover inside out, and it's done.
Repeat for each heating pad.
Put your heating pad in its cover and enjoy!