Yes

Thank you Sheilajoyce. I'm sure it seemed like a dumb question, but I wanted to be sure.

Have you read all the way through the pattern? Usually the heel flap is done on half the stitches. The other half are placed on a holder at that point.

I do my flap by doing a slip 1, knit 1 on the RS row and slip 1 purl 1 on the WS row.

It tightens things up a bit and shapes around the angle. Otherwise, you have more of a tube shape to the sock.

Thanks Yarnlover. I'll let you know how it turns out.

I also wondered about a heel flap that's knitted in plain stockinette stitch. Usually, they're knitted in a pattern that gives more shaping and reinforcement to the heel area, such as the one yarnlover describes, or the one described in the Christmas stocking thread below.

I knitted this in stockinette stitch because that's what the pattern said, but next time I will do it as yarnlover describes.