Thursday, December 1, 2016

Corrugated ribbing tricks and tips

Corrugated ribbing looks like a very fancy kind of ribbing and it's knitted like a fancy kind of ribbing, but doesn't act much like a ribbing at all.

Front and back of a simple 2-color corrugated 1/1 ribbing. 15 columns are shown: 8 knits, 7 purls.

Admittedly gorgeous, corrugated ribbing is certainly traditional for certain kinds of Fair-Isle knitting. Yet, structurally speaking, corrugated ribbing is a rather poor choice at a garment edge.  It also has certain other peculiarities which can detract from its overall appearance.

Today's post starts out with a background on the problem, then turns to some tricks and tips you may find useful in designing or knitting with corrugated knitting.


Ordinary ribbing, knit in the same yarn, and a far LOOSER gauge than above corrugated sample.  Like the opening photo, this close-up also shows a piece 15 columns wide: 8 knit and 7 (hidden on the back!) purl columns.  Note how much narrower this sample is than the previous--this is because ordinary ribbing such as this "draws in."
Ordinary ribbing is a highly three-dimensional fabric with a great deal of "reserve stretch" built into the fabric.  Corrugated ribbing is the opposite: non-stretchy, it does not "draw in."  Ordinary ribbing helps garments cling around cuffs and bottom-bands.  Corrugated ribbing does not cling at all. So, why is corrugated ribbing called "ribbing" at all?

Structurally,  the basic idea behind corrugated ribbing is alternating columns of knits and purls, so in its manner of construction, corrugated ribbing does resemble ordinary ribbing.  Also similar to ordinary ribbing, corrugated ribbing can be worked in various arrangements of knit and purl columns: 1/1, 2/2, 2/1,* etc.

However, although they are knit similarly, the two fabrics have very different types of structure, and this is because of color-knitting.  You see, ordinary ribbing is one-color knitting, but corrugated ribbing is a form of two-color knitting.

Two-color knitting requires the color not in use to be "carried" or "floated" across the fabric back.  It is all those floats back there which stop corrugated ribbing from stretching when pulled.  The upshot is that ordinary ribbing--well known as a stretchy fabric--becomes a firmer fabric when knit as two-color corrugated ribbing.

Although the two photos above show the ordinary ribbing to be narrower, this is true only when the two fabrics are at rest. The surprising fact is, the corrugated ribbing is actually the narrower fabric overall.  When stretched, ordinary ribbing can become MUCH wider than corrugated ribbing, despite the opposite being true when both fabrics are at rest. Again, this is due to the "reserve stretch" built into the ordinary ribbing, which is absent from the corrugated ribbing.

Another key structural difference between corrugated ribbing and ordinary ribbing is that ordinary ribbing is a non-curling fabric.  Recall that fabrics featuring a distribution of knit and purl stitches on each fabric face (so called "reversible" fabrics) do not curl. In fact, even if the distribution is as low as 75% one kind of stitch to 25% of the other kind, the fabric is essentially curl-free.  Ribbing meets this definition by its alternating columns of knits and purls, and even a 3/1 ribbing will not curl.  However, despite the fact that corrugated ribbing is worked up in alternating columns of knits and purls, adding the floats from two-color knitting into the mix upsets the reversible nature of the fabric.  In other words, the floats on the back unbalance the fabric.  Result?  Corrugated ribbing can curl and flip and get up to all the miserable little tricks that stockinette fabric does.

property ribbing corrugated ribbing
possibility for 
different configurations (1/1, 2/1 etc)
stretches, “draws in”

flips up, curls up

beauty of appearance:

Above is a chart summarizing the similarities and differences.  Below, I address the issues raised.


Because ribbing stretches and corrugated ribbing does not, you must knit corrugated ribbing to different rules than ordinary ribbing.

Specifically, ordinary ribbing is generally worked on fewer stitches than the main body of the garment, and using smaller needles.  By contrast, corrugated ribbing is generally worked on the same number of stitches as the main body of the garment, and using the same sized needles.  Failure to make this adjustment will result in tight, unpopular  sweater bands.


Problem 1:
Corrugated ribbing is quite firm.  Casting on for a firm fabric is quite the trick.  Too loose and you get flare, too tight and you get puckers. Plus, a tight cast-on--with the yarn held under constant stress--wears out oh so much faster than it should.  (I think wear-through from a too-tight cast-on/off probably spells the end to more high-use sweaters than any other problem, including outgrowing them or wearing out the elbows.)

Problem 2:
While ordinary ribbing does not flip or curl,  corrugated ribbing tends to. Sometimes, this leads to peek-out, where the back face of the fabric, with all its floats, peeks out at the bottom of that gorgeous Fair-Isle sweater you knit.

The solution I propose solves both problems by separating the edge of the fabric (where the structural problems lie) from the edge of the garment--where you want your corrugated ribbing to appear in all its glory. TECHknitting blog already features a whole post on separating the edge of the fabric from the edge of the garment, so I won't go into all that again here, but all boiled down, my advice is threefold:

  1. cast on in any manner you like, somewhat loosely.
  2. Knit several rounds (3-5, or even more, depending on taste) in stockinette.  This not only creates a sturdy rolled edge, but it also hides the cast on
  3. Above the rolled edge, knit two or three rounds in main color, working in the ribbing which corresponds to your proposed corrugated ribbing.  (1/1 ribbing if you'll be knitting 1/1 corrugated, 2/2 if 2/2, etc)

The result is, the corrugated ribbing--not well suited to be a fabric edge--gets bordered with a structurally correct edge: a garment-edge which can take wear, yet will not flip, flare or bind. Furthermore, this bottom edge is much shorter than the number of rows suggests, because the rolled edge curls up to hide the few rows of main-color ribbing.  The effect is to create a short textured frame in main color, laying just below the start of the corrugated ribbing. Here's another view of the opening photo with its rolled edge

Just as a picture frame does not hide the bottom of the painting, but rather, sets it off, so a frame of main color does not hide that the "visual bottom" of the garment is the corrugated ribbing itself. Also by this trick, the floats on the back are so far up and in from the garment edge, that they will never peek out from the bottom, either.  

If you do not care for the look of a rolled edge, you can achieve many of these aims by simply casting on and working a few rounds in main color ribbing before beginning the corrugated ribbing.  However, you then may find that the flip wants to occur at the border of the ribbing and the corrugated ribbing, so consider using the transition zone trick to help mitigate. Swatch first, of course.

Multiple pass knitting as an option

Corrugated ribbing resembles ordinary ribbing in this at least: it is created by working alternating columns of knits and purls.  Corrugated ribbing is also a form of two-color knitting, so you must control two separate yarns, applying each to the correct column. I believe two-color knitting goes fastest and works easiest when you hold one color in each hand.

However, even if you are perfectly at home knitting stockinette in two colors, you may find that alternating knits and purls with one color in each hand is not that much fun.  If so, I have a trick that will let you apply only one color at a time, making it much more feasible to work corrugated knitting in front of the TV, for example, or on your daily bus-commute. This trick is called "multiple-pass color knitting"

Multiple-pass knitting
The link above takes you to a whole post about how to work multiple pass color knitting, so I won't repeat all that.  The short version is, you work one yarn at a time, IGNORING the stitches worked in the other color.  This requires you to go through each round TWICE, first working in one color, then the other. How you do this is, you slip out of your way the stitches you're ignoring, without operating upon them, and work only the stitches in the same color as your yarn.

Example: in a black garment with colorful corrugations, you might work the black yarn in the first pass, knitting or purling it as your pattern requires.  Each time you come to a non-black stitch, you hold the black yarn to the back, then simply slip the non-black stitch from the left (holding) needle to the right needle without changing the stitch orientation. In this manner you go around, working the black yarn until you finish the round.  Naturally, the round is only half-done, and you now go back for the second half of the round, working the other color yarn as required and slipping the black yarn.

Note that if you choose to do this trick, you should always work the same yarn first--in our example, the black one.  Otherwise, the fabric gets subtle but odd stripes where the "other yarn" broke pattern and went first. Also, don't stop at the half-way point: make it a rule for yourself that you have to do BOTH passes through the fabric before quitting for the night.

Note also that ALL color knitting can be done this way, not just corrugated ribbing, and that you're not limited to two colors: you can pass through as many times as you like, with as many colors as you want (although, of course, your fabric back will become very thick from all the floats).


Some people (myself among them) do not care for the look of the contrasting-color dot which occurs when purling in the first row of a color change.  I have called these blips "icky dots," and wrote a whole blog post about how to avoid them. However, tastes differ,  and in all things, it is "knitter's choice."  (And, even I must admit that sometimesblips can be a beautiful design element**)

Below is a corrugated ribbing knit with a color change in every row, where the corrugations appear in the colorful columns.  Specifically, the ribbing is 1/1, the color changes are worked every row, the colored columns are the purled ones, while the black columns are the knit ones.  Have a look and you will see what I mean by "blips" (icky dots).

"Blipped" ("icky dot") corrugated, where every row in the colorful columns is worked as a different color, as a purled stitch

To my eyes, working every colorful row as a purl stitch in corrugated ribbing, as in the above examples, makes for a rather muddy transition.  Yet, I must admit that I've knit a sort of worst-case scenario.  For one thing, the colors transitioning here contain strong contrasts. Colors more closely related would look better blipped together like this.  Also, if there were more than one row of each color, the transitions would be a lower proportion of the overall work, which would mitigate the effect somewhat. Swatch, swatch, swatch, and see for yourself how YOU like the blips arising from purling every colorful row in a corrugated ribbing.

If you decide you don't mind the blips, no need to read further in today's post.  However, if you wish to AVOID blips, then read on--below are three tricks to do so.


Recall that the whole problem with contrasting color blips (icky dots) is caused when purling in a new row of a color change.  The act of purling drags up into the current row, the "head" of the stitch in the row below.  These little stitch-heads positioned next to one another along the row are the "icky dots."  Therefore, one cure is to avoid purling on the first row of a color change.  There are three ways of effecting this, each considered below.

Trick #1: Work the purl columns in the main color, instead of in the contrast color. 
If you reverse the usual order of the corrugations by working the "purl columns" in the main color, and the color-change columns in knit stitches, the purl stitches are always in the SAME color (the main color) so there is no opportunity for blip-formation.  Meanwhile, the color-change columns are in knit stitches, which do not form blips. Therefore, you can change the colors in the color-change columns as often as every single row, if you like, and there will never be a problem with blips.  This was done in the opening photo (first photo of post).  Below is an additional example.

The black columns (main color columns) separating the colorful columns are worked in purl, and in this way, the over all "corrugated" texture is preserved, yet the colorful columns, being knit, show no "blips" ("icky dots").  Compare this photo to the previous.
For a further example of corrugation in the main color columns, here is a link to a beautifully-knit corrugated 2/2 ribbing with frequent color changes, where the knitter worked the main color (black) as the purl stitches, and the colored stitches as the knit ones. BTW? the linked picture comes from Feral Knitter's blog whose post about corrugated ribbing shows some other lovely experiments in this same mode. (She's got a book about Fair Isle knitting out too.)

Trick #2: When working in two colors only
If you knit corrugated ribbing in two colors only--one main color, and one contrasting color AND if the corrugations (purls) are in the contrasting color columns, then the blips would only show at the top and bottom of the contrasting color columns, as shown in this linked sample. The cure is simple: in the first of the corrugation-rows and the first row of the knitting ABOVE the end of the corrugation-columns, work every stitch so it appears as a knit stitch on the front fabric face. No purling, no blip.

Trick #3: Two rounds high (my favorite trick)
If you want to work in many colors with the corrugations in the colored columns, but want to avoid the blip, use this trick: work the purl columns so that each color is two rounds high, the first round knit, the second purled.  In this way, when the act of purling pulls the head of the underlying stitch into the current row, it makes no blip because the underlying row is the same color. Stated otherwise, make each "row" of corrugated color actually TWO rounds high, knitting the first round and purling the second round. Below are two examples--compare these to the "blipped" corrugated shown earlier, and also to the sample where the corrugations are in the main-color columns. 

Two examples of 2-row-high "blipless" corrugated, worked as described in the text.  Note also the rolled edge evident on the white sample.

This 2-round high trick is my favorite, and I use it almost exclusively when knitting multiple colors in corrugated ribbing.  This is partly because I think the corrugations look more impressive when worked in the colors, rather than the main color; partly because I like the "centered" look when each color is worked 2-rounds high with a little texture dot right in the middle of each little color-square; and partly because I am lazy. 

You see, this two-row-high trick makes working corrugated knitting easier, because the net effect is to reduce purling to a mere 25% of your total fabric. Also, if you were working the multiple pass knitting method mentioned above in a bid to avoid two-color purling, you'd only have to slip once out of every two rounds, instead of every round. This 75%-25% ratio would also make this the easiest modification of corrugated ribbing to knit flat (back and forth).

Have fun with this--

Addendum, Dec 22 2016: Juliane L. wrote me via Hotmail (address in R sidebar) to say the following:

Here's something you made me realize: with multipass knitting for corrugated rib in the round, you don't need to purl ever. Just do the knit-color round as normal, and the purl-color round in the other direction, looking at the inside, and slipping with yarn in front.

The knit stitch, yarn in front alternation still makes you switch the yarn from front to back, so this is probably useless for yarn-in-the-right knitters, but for continental, it works great. I do rounds on two circs, and there you only have to pick up a new needle as often as for one single-pass round, not as for two: at the end of the knit-color round, just turn the needle to begin the purl-color round and vice versa.

Only trouble is to keep the yarn from the resting ball from getting trapped where it shouldn't while changing needles.

Thank you for writing, Jule, this is a wonderful idea.  It made me slap my head and say "of course!"  Best regards, TK

*1/1, 2/2 and similar notation is a shorthand for describing ribbing, and here is the key. Assuming you are working in circular knitting...
  • 1/1= on an even number of stitches, k1, p1 every round 
  • 2/2 = on a multiple of 4 stitches, k2, p2 every round 
  • 2/1= on a multiple of three stitches, k2, p1 every round
and so on...


** The linked photo is to a sweater knit in "bohus" style, which cleverly uses purl blips to set off the gorgeous color designs.