Gee, you have asked me a good question. Here is what the directions say for the slippers..
Materials: For women's size: Double knitting (DK) pure new wool, 1 3/4 oz balls.
Just by reading that I still can't tell if its the yarn or the method. What do you think? The slippers do not look thick. Looks more like a worsted weight yarn to me..but I really can't tell.
The book is Knit handmade style by Janine Flew. There are beautiful blue and white slippers in this book and thats the reason why I recently purchased tthe book.
If you see the link below and click on the picture of the book they even show the pretty slippers there in blue and white.
Thanks again for any clarification you can give me.