Took one look and knew it was a tucked brioche variation - and I couldn't resist swatching right away to duplicate the look.
Here's my version of the stitch - I call it Chicken and Waffles - one side looks like a waffle stitch (bulky yarn) and the other side looks like chicken tracks (to me anyway).
My version is a variation of brioche rib using a fingering weight sock yarn and a bulky yarn. It's fun and fast once you get the technique done and the resulting ribbed fabric is really cozy yet sporty.
I use the brioche terminology developed by Nancy Marchant in her book, Knitting Brioche. See below for the non-standard definition - let me know if something isn't clear. Worked flat, using US size 9 needles
Cast on odd number of sts in fingering weight (fw). This includes 2 edge sts kept in garter.
Set up Row (fw) - p1, (k1, p1) to end
Row 1 (bulky) - k1, (sl1yof, k1) to last st, k1
Row 2,(bulky) - k1 (sl1+yof, p1) to last st, k1Row 3 (fw) - k1, (brp+1, sl1yof) to last st, k1
Row 4 (fw) - k1, (k1, brp1) to last st, k1Rep rows 1-4
I think I will go down a needle size or 2 next time.
Sl1yof - slip 1 st purlwise, take working yarn over the right needle and back to the front.
Sl1+yof - slip 1 st purlwise and the yarn over wrap from the previous row, take working yarn over the right needle and back to the front.
Brp - brioche purl - purl together the slipped st and the yarn over wrap from the previous row.
Brp+1 - purl the slipped st and the 2 yarn over wraps from the previous row.
I will be developing a cowl pattern for this that is worked in the round. Here's the inspiration cowl that got me started.