Jami at An Oregon Cottage: "My whole family loves using these easy-to-make flax seed pillows for everything from sore necks to foot warmers (on cold nights it’s a treat to slide into bed with warm toes!). And they have been one of the most popular gifts I have given as well as one of the most popular things I sold when I had a craft business."
This project is EASY to sew. Flaxseed is the best filler for your neck-warmer, foot-warmer, whatever-warmer for a number of reasons. In the video Jami describes why it's superior to rice, corn, husks, etc.
For the whole list of what makes flaxseed the best and all the steps, plus a link for free printable tags, see this article on An Oregon Cottage: