You're humming along on a gorgeous lace shawl or a fitted sweater sleeve. Everything looks great until the pattern demands a purl 2 together thru back loop. You pause. Your needles feel like clumsy chopsticks. Honestly, this is the one stitch that makes even seasoned knitters want to put their project in "time out" for a week.
It’s awkward. It’s tight. It’s the p2tog tbl.
Most people dread it because it feels like you're trying to perform surgery through a keyhole. But if you want your knitting to look professional, you can't just skip it or swap it for a standard purl two together (p2tog). They aren't the same. While a p2tog leans to the right on the knit side, the purl 2 together thru back loop creates a crisp, left-leaning decrease on the "public" side of your work. It’s the mirror image your project needs for symmetry.
Why Does This Stitch Even Exist?
Knitting is all about geometry. When you decrease on the purl side (the "wrong side"), you’re usually doing it to affect how the stitches look on the knit side (the "right side").
Think about a V-neck sweater. To get those beautiful diagonal lines that frame your neck, you need the stitches to lean toward the center. If you only knew how to p2tog, one side of your neck would look flawless and the other would look like a jagged mess. The purl 2 together thru back loop is the unsung hero that fixes that. It twists the stitches just enough so that when you flip the fabric over, the decrease slants exactly where it’s supposed to.
It’s about balance.
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Breaking Down the Mechanics
Let’s be real: the physical act of doing a purl 2 together thru back loop is a bit of a finger-twister. Usually, when you purl, your needle goes into the front of the loop from right to left. Easy. For this version, you have to bring your right needle behind the left needle and poke it into the back legs of the next two stitches.
It feels wrong. Your hands will tell you it’s impossible.
Here is the trick that expert knitters like Elizabeth Zimmermann or the folks over at Purl Soho often hint at: it’s all about the tension. If you knit tightly, you are going to struggle. Hard. Before you even attempt the stitch, use your right needle tip to loosen the next two stitches on your left needle. Give them a little tug. It creates the slack you need to maneuver that needle tip into the "back door" of the loops.
- Bring your yarn to the front (as you always do for purling).
- Reach your right needle tip behind the left needle.
- Insert the tip into the back loops of the first two stitches on the left needle, going from left to right.
- Wrap the yarn and pull it through.
It’s a tight squeeze. Sometimes, it helps to tilt the tips of your needles toward your chest so you can actually see the back of the loops.
The "Cheat" Method: Slip, Slip, Purl
If the traditional purl 2 together thru back loop makes your wrists ache, there is a legitimate alternative that gives you the exact same result. It’s called the SSP (Slip, Slip, Purl).
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Technically, they are sisters.
To do an SSP, you slip the first stitch knitwise, slip the second stitch knitwise, and then return them to the left needle. By doing this, you've manually changed the "mount" of the stitches—basically, you've untwisted them. Now, you can purl them together through the back loops much more easily because the path is cleared. Some purists argue it’s a different stitch, but in the context of a modern pattern, the visual result on the right side is identical. It’s a left-leaning decrease. Period.
Common Pitfalls and How to Avoid Them
The biggest mistake? Splitting the yarn. Because you’re working blindly behind the needle, it’s incredibly easy to shove your needle tip right through the middle of the fiber instead of through the loop.
Check your work.
After you finish the stitch, flip your knitting over to the right side. Does the decrease look smooth? Or does it look like a tangled knot? If it looks messy, you likely grabbed only one of the two back loops, or you accidentally twisted the yarn wrap.
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Another issue is stitch distortion. Because this stitch requires a lot of pulling, the resulting stitch can sometimes look "long" or "loose" compared to its neighbors. To fix this, make sure you aren't pulling the yarn too far away from the needles when you wrap it. Keep your movements small.
When to Use This (and When to Skip It)
You’ll see the purl 2 together thru back loop most often in lace charts. Lace is the ultimate test of a knitter's patience because it relies on "decreases over yarn overs." If your decrease leans the wrong way, the entire geometric pattern of the lace shifts. It looks "off," even if you can't quite put your finger on why.
It’s also vital for "full-fashioned" shaping in garment construction. If you’re knitting a sweater in the round and you reach the underarm, you’ll often use these decreases to create a professional-looking seam line.
Can you skip it? Sure, if you don't mind a slightly "homemade" look. But if you want that high-end, boutique-finish appearance, you’ve got to master the back loop.
Actionable Steps for Mastery
Don't wait until you're in the middle of a $200 cashmere project to try this.
- Practice on scrap yarn: Grab some bulky wool and 5mm needles. The larger the scale, the easier it is to see what’s happening. Spend ten minutes just doing row after row of purl 2 together thru back loop.
- Use pointy needles: If you usually use blunt wooden needles, switch to "lace tip" metal needles (like ChiaoGoo or Addi Rockets). The sharper point makes it significantly easier to dig into those back loops without splitting the yarn.
- Watch the right side: Every time you complete the stitch on the purl side, flip it over immediately. Train your eye to recognize the left-leaning slant on the knit side. Once you see the "why," the "how" becomes much less annoying.
- Loosen up: If you’re a tight knitter, conscious relaxation is your best friend here. Drop your shoulders. Don't strangle the needles. The extra millimeter of slack makes all the difference.
Mastering the purl 2 together thru back loop is basically a rite of passage. It marks the transition from a hobbyist who follows instructions to a knitter who understands the architecture of fabric. It’s uncomfortable at first, sure, but the results speak for themselves in the crisp lines of your finished garment.