This is an extra warm lined mitten. The seersucker stitch pattern on the outer mitten make it extra squishy and warm. Add the soft lining and you have a mitten to withstand the coldest of temps. I used a worsted weight yarn for the outer. Any sport or sock weight yarn is good for the lining. The yarn I chose was a variegated color so it appears that the lining is a different color for the right and left mitten. But I think that adds to the uniqueness of the mitten. The lining is attached simply by picking up stitches inside the ribbed cuff on the outer mitten when the outer mitten is complete. This is nice if you finish the outer mittens and then change your mind and want to leave as is. The lining is completely optional.