The flax seed helps retain the heat for about 20 minutes when the pads are microwaved for 2:30 minutes. They shouldn’t be microwaved for more than that; 2:30 provides a pretty warm heating pad, any longer could scorch the fabric and hurt the wearer (ask me how I know!!). I’ve made these with “channels” so that the flax seed is a bit more stable, stays in place rather than settling in one area of the pad. The curved shape helps the pad to stay on the shoulders. It also works well to heat the lower back and abdomen, really anywhere you want heat to help relax muscles. Just don’t wear it for much longer than 20 minutes!
These are NOT machine washable; they can be gently spot cleaned with a soft wash cloth or rag and air dried. I’m not really sure what would happen to the flax seed if exposed to water for a long time; I use crushed flax seeds in baking; after soaking some in water, it becomes a bit congealed. We don’t want that happening in the heating pad!!