This is faux rib. On the front side, it looks like stockinette when it is relaxed. When stretched horizonatally, the rib effect shows. The reverse side looks like all purl stitches.
Repeat Rows 1 - 2
Row #SideBegin RowRepeatRepeat From *
1Rk1*sl 1 wyib, k1*
2Wk1*p1, k1*
Row: 2  
  Row: 1