I reinforce heels and toes in all socks I knit. "Always" -- which means it's my rule (but exceptions can be found).
Back when I first started knitting socks, I considered it mission critical to buy the little cards of reinforcing thread sold in a range of colors to match most yarns. I was in graduate school when the passion for sock knitting really took hold of me. And with a grad student's income, it wasn't long before I decided that, relatively speaking, reinforcing thread was expensive. Too expensive.
Pictured above are just the cards I have left. The sticker prices range from $2.50 to $3.50 per card (the last I bought would have been at least four years ago, so those are old prices). At two cards per pair of socks, reinforcing thread tacked an additional $10-$14 onto the cost of my "affordable little projects."
About four years ago, I picked up several skeins of Moscow Yarn Company's wool in two lace weights Ksenia (cobweb) and Lydia (even finer cobweb). I found them at A New Yarn, the non-profit yarn store I adored which sold both new and donated yarns -- you could find amazing things there until they closed in Spring 2009. I didn't have a project in mind, but at $1 per skein figured I'd come up with a nice shawl pattern someday. The wool went into my stash, where it sat for awhile.
One day I wanted to start a pair of socks but didn’t have matching reinforcing thread on hand. I was looking around for somethind else that might work and remembered the Moscow Yarn Company wool. At such a light weight and with a nice twist, it held up in comparison to the cards I did have on-hand and seemed like a good substitute.
I've never looked back. The darker, Lydia, is my favorite. In fact, I use it pretty much exclusively now. And whenever I teach sock classes, I invite my students to wind off enough for their projects, too. It’s performed really really well and saved me a ton of money. I haven't even finished off one skein's worth yet. Plus, because it’s already put-up in a center-pull format, it’s really convenient for me to pack two skeins in with my sock project pack and just knit off what I need.
The darker grey color works equally well when in contrast to the base yarn...
On Stripes of Sunshine I experimented with reinforcing toes only
so I could see how well the Eye of Partridge heel stitch
holds up on its own. (The answer is "very well.")
I expected it to show up more and was surprised
by how little contrast it ended up having.
On the Twin Rib socks I made my Mom in December,
the contrast is more apparent yet still looked
as if it had been designed expressly to go with the Regia Bamboo.
... as when in harmony with the base yarn....
I can't even see it on the Country Garden socks, can you?
The only thing giving it away on the Marshlands Lace Rib is the denser fabric
where the reinforcing wool is used. I suppose you can see a hint
as if outlining some of the lighter colored stitches on the heel.
It wears like iron. I haven't worn through any of the toes or heels on socks reinforced with it yet -- and unless I'm wearing gym shoes, the only socks that go on my feet are handknits. I may have mentioned before that as a die-hard fan of heeled boots, I'm pretty hard on my socks. Toes, especially.
But there’s nothing particularly special about the Moscow Yarn Company wool for reinforcing except that it's what I have in my knitting bag at all times and that the dark grey truly does blend nicely with everything I’ve made. I don't even bother to take this yarn out of my bag. It's always at-the-ready.
As far as I'm concerned, you could use just about any nice lace-weight wool and be happy with it. You probably have something sitting in your stash already that’s left-over from another project and more-than-enough to keep you in toes and heels for awhile.
In fact, I have another couple of wools that I also picked up from A New Yarn once I figured out this little trick.
As you can guess, I haven't felt the need to use them yet, so I can't say how the 2/20 weaving worsted performs. I can say that the mustard one held up remarkably well to the playful assault of my cardboard-chewing cat, Mouse, when the tube skidded under the bed during the week of our move... although it did lose its label!