This got me thinking about how it's fairly standard practice to reinforce the back of the heel when knitting socks. But how? The most common way that I've encountered to reinforce the heel is to work every right side row of the heel flap (Slip 1, Knit 1) repeated to the end of the row, and simply purl the wrong side rows. It looks a little something like this...
The result is a firm fabric, slightly thicker than stockinette, with every other column of stitches backed up by a strand of yarn carried along behind it. It's easy to see why this is the most popular method of reinforcement--nothing difficult, no extra needles, yarn, or sewing involved. But what if you want the simplicity of stockinette?
I found myself in this situation with the socks I'm knitting that have been dubbed the "Powder 8's". I chose a variation on what Nancy Bush calls the "Balbriggan Heel" in Folk Socks--a simple heel with no short rows (but with Kitchner stitch--probably an equal trade off) that complemented the cables I wanted to run down the heel flap.
The most straightforward way to reinforce a heel flap done in stockinette is to hold two strands of your sock yarn. Pros: no additional materials required and no 'post mortem' work required (i.e. reinforcement occurs during normal knitting). Cons: Changes gauge and may be overly thick.
A variation on this method is to add a strand of nylon thread instead of a second strand of yarn, and this eliminates the cons of changing the gauge and increasing the thickness. Unfortunately, it also negates the pro of no additional materials required.
Another way to reinforce your stockinette heel flap is to again use two strands of your sock yarn and alternate the strands of yarn for each stitch (i.e. Yarn A used for stitch 1, Yarn B used for stitch 2, Yarn A used for stitch 3, Yarn B used for stitch 4, etc.). Pros: no additional materials required, no 'post mortem' work, and theoretically no change in gauge. Cons: all of the difficulty and tedium associated with two color-knitting without the benefit of two-colors--stitch non-uniformity will be more obvious.
The last method for your consideration is to thread yarn through alternating purl bumps on the wrong side of the heel flap. This is the method I settled on for my pair of the Powder 8's. Choose where the area you want to reinforce, and using a tapestry needle, thread a strand of leftover sock yarn under a column of alternating purl bumps:
When you reach the top of the area that needs reinforcement, turn around and thread through the next column of purl bumps, threading through the rows that you skipped on the previous round:
Repeat until desired area is covered. Pros: doesn't change gauge or stitch uniformity. Cons: requires 'post-mortem' work--if you hate weaving in yarn ends, this isn't the technique for you.
I think I may even start reinforcing all the main points of contact on the foot--the back of the heel, the bottom of the heel, and the ball of the foot. My Smartwools affirm wear on the ball as well:
I guess I should be impressed that they've lasted this long. Still, I'll miss them when they disintegrate off of my feet.