Laine Saint-Pierre has been part of Sajou's Fil au Chinois for many decades. It is strong darning wool made of four strands. It is also used for a wide range of embroidery projects.
It is made of 50% wool, 50% polyamide and it is very solid and easy to use, unlike some other (cheaper!) darning wools which twist and knot as you work with them. They are certainly worth the price difference.
The colours remain fast and there is a great selection of 96 colours to choose from.