These are Norwegian twined mittens that have the purl side out. Instructions are given for lining these using either a “napping” or “shagging” technique.
There is no specific yarn suggested, but amounts in ounces are given for each of the sizes. A worsted weight wool yarn is suggested for the mitten itself (3-5 ounces, depending on size pattern), and a soft sport weight yarn is suggested for the lining (1-4 ounces depending on the pattern size and lining technique chosen).
Degree of difficulty is listed as 3 out of 4 mittens, challenging and exciting.