This winter my family was cold, so I found the softest worn-out sheets in our mending pile, and sewed microwaveable warm packs that hold heat for a long time. I filled them with dry rice, and added herbs or spices. It takes about 10-15 mins to cut, sew and fill.
I had fun adding herbs and spices to them to create lots of smells. Deciding what spices to put in is like cooking. I've made one with lavender, one with a mixture of Indian-inspired spices that reminds us of Indian sweets, another with cumin, black coriander, bay leaves, & pepper, and some other experiments. Or you can leave out the spices if you want to keep it simpler.
There are lots of instructables for neck, hand, and other warmers made from fabric and heatable fillers. I've included mine because I wanted to emphasize how much fun you can have creating a spice mixture, how you can use almost any kind of fabric, and to give detailed sewing instructions for a handy multi-purpose size.
Worn-out sheets and pillowcases are great; you can use any fabric you want. Worn-out things around the house are soft and smooth, such as flannel from nightclothes or knits from old T-shirts. Of course you can use new yard goods. This project shows one made from an old sheet, one from a T-shirt, and one from some soft old towels.
Step 1: Gather Materials
Gather up fabric (you will need either big scraps from an old sheet or pillowcase, or fabrics that you can cut pieces of about 8" by 12"). Any kind of rice, you will need 1.5 to 2 lbs (3 to 4 cups). Scissors, sewing thread and machine. A ruler is helpful but you can eyeball the measurements. Optionally you can enjoy putting in spices. I have used lavender, mixtures of whole culinary spices, herbs, and seeds that I have cracked or ground in a small grinder, vanilla pods, and pre-ground spices.
Step 2: Cut and Sew
If you are using an old, threadbare sheet (the best texture!), then you should have a double layer of fabric to prevent rice from escaping and make it feel like a good thickness. Cut a piece about 12" wide and about 33" long. No need to be precise. Fold in half to bring the 12" edges together, making a 12" by 16" rectangle. Fold the 12" edges together again to form a 12" x 8.5" rectangle. Sew on a machine around the edges, with acout 1 com seam allowance, leaving 4" unsewed at the end as turning and filling hole. Remember to lock the stitching at the beginning and the end. (To lock, sew back and forth over the same stitching for 1/4 to 1/2 inch).
If you have thicker or stronger fabric, then just use one layer. Cut 12" by 17" and fold once. Or cut two separate pieces about 12" x 8". Remember to put WRONG sides of fabric together before sewing, because the RIGHT sides come to the outside when it is turned inside out.
I have used black thread here for contrast, but you may prefer to use matching thread.
Trim corners and trim edges except along the filler hole.
Turn inside out, pushing out corners with your fingers to form a soft rectangle.
Step 3: Fill With Rice and Spices
Use 1.5 to 2 lbs of rice (3 to 4 cups) depending on how firm or flexible you want your heating pad to be. You don't really have to measure it like I have done, but I find the pyrex pitcher very convenient for pouring into the heater. You could just pour the rice in from the bag, or use a funnel with a wide enough spout.
Decide on your herbs and spices. This is the fun part. Lavender is classic from many traditions. Or choose whole spices, seeds, and herbs. Or choose pre-ground spices. Use whatever you have at home. You can add them whole, loosely crack them with a hammer or back of a spoon, or crack or grind them in a spice grinder. For this heater I choose Bay Leaves, Black Pepper, Black Cardamom, and Cumin Seeds lightly cracked in a grinder. I put about 2 tablespoons of spices in. I let them mix with the rice as I pour, but you can drop them in later, and mix them by kneading the bag.
Step 4: Finish Sewing
Turn the raw edges of the filler hole under neatly, and sew with machine, locking both ends. You also could blindstitch by hand, but why bother, unless you are trying to make a very elegant gift heater.
Step 5: Microwave
Microwave for 2 to 3 minutes. It will stay warm for at least 30 mins! Put it on your shoulder, in bed with you, under your feet where you sit, sit on it, put it on your back while sitting or lying down... you will find many uses in the winter.
You can microwave as many times as you want. The rice put out some moisture at first, which is nice, and eventually dries out but still heats.
You can also put these in the freezer for a cool pack, but that's a different contest...
Step 6: Other Fabrics
You can also use single thickness of fabric. Depending on what you have available, either cut a long piece to fold, or cut two 12" x 8.5" pieces. Remember to match them with RIGHT sides together before sewing, because you will be turning them inside out.
These pictures show three heaters. Here are the fabrics and spices:
1. Two pieces of old towel with short grain rice, plus diced vanilla bean, pinch ground cinnamon, ground dried ginger.
2. Old sheets, double-thickness fabric, short-grain rice, bay leaves, black cardamom, cumin seeds, black pepper.
3. Front and back of child's outgrown tee-shirt, jasmine rice.