These rugs were originally used in boats and sleighs as well as in beds to keep the traveller or sleeper warm. Later they were used on beds and the decorativeness was getting more important.
Here you see the structure of the ryijy rug, worn in heavy use. Blogger turned my picture again.
A new use was in the church for the wedding pair to kneel on, and the rugs were decorated with many symbols like the tree of life. The most beautiful rugs were then hung on the wall or used on benches or rocking chairs. During the first decades of last century many patterns were created by artists and sold through Suomen Käsityön Ystävät, the Friends of Finnish Handicraft.
Later a popular way of making your own ryijy without a loom was to use a woven base and a needle to make the knots. I remember my mother making cushion covers with this method.
Here is an example of a modern ryijy rug, designed by Raija Rastas:
See the close-up and the lovely variety of threads.
You can see more examples on the site of the Friends of Finnish Handicraft.
I will try to find the unfinished cushion cover I have from my mother, and make some pictures for you to see.