I’ve been asked quite a few times about suitable yarn substitutions for these two designs (one from Knitty and one from Stitch ‘n Bitch). Both of these sweaters, since they had their genesis in the same design concept, use the same gauge yarn, namely, “chunky” yarn that knits at roughly 14 sts and 20 or 21 rows per four inches (any gauge difference between the patterns is probably a blocking-induced gauge change).
In general, here’s a wonderful (ha ha) article on choosing suitable yarn substitutions.
More specifically, there are a lot of suitable substitution yarns available for these two patterns. Because of their plain, easy-fitting design, and the simplicity of the cable in Big Sack, you can choose soft yarns or harder yarns, smooth textured yarns or fuzzy yarns; it’s really a choice to be dictated by your wallet and your own preferences. Peruse your real or virtual LYS for yarns with the right gauge, and decide what you feel like knitting.
Having said that, here are a few guidelines.
If you’re planning to use an animal fiber:
Think about how you’re planning to wear the sweater. If you mean to wear the sweater as your outer layer defence against the elements, you won’t mind if the yarn is scratchy, which means that the Tahki Soho Bulky and Alafoss/Reynolds Lopi are suitable yarns. Soho, and tweedy yarns like it, lend a rustic look to your sweater. Lopi is usually solid (there are some heathered colours) and result in an outdoorsy-but-not-quite-rustic look. Both of these yarns are twisted singles, and to my touch the Lopi is less comfortable for direct skin contact. Soho isn’t all that soft, but soft enough for me so that I can wear Banff over a t-shirt; I have relatively high “itch” tolerance. I’ve found from knitting both these yarns that despite the fact that it’s a twisted single, the Soho is less energized than than Lopi; my stitches in Soho aren’t as skewed as in Lopi. (Read up on energized singles and spinning if you don’t know what I mean.)
Yarns like these create a beefy, thick fabric. It could potentially be quite a heavy fabric, depending on how dense your knitting actually is. Other yarns that behave in a similar manner include Rowanspun Chunky (the yarn used for Big Sack; I have issues with it, below), Rowan Yorkshire Tweed Chunky (the manufacturer’s suggested gauge is just a guide, remember), Patons Upcountry, and a lot more–too many to think of and list. If you’re looking in your (real, not virtual) LYS for a substitute like this, grab one of these suggested yarns and compare its construction, feel, and thickness with potential substitutes.
A side note: since knitting the Big Sack, I’ve determined I’m not that fond of Rowanspun yarns–I find the “pre-fulled” aspect of the yarn somewhat distracting. If I knit a garment from woolen-spun yarn, I want it to acquire that fulled look after washing, to create a unified fabric. Somehow, the fabric’s not the same when using Rowanspun. I like the Rowan yarns with the more traditional plied construction like Magpie and Chunky Tweed, both discontinued. (Chunky Tweed is another good substitute for these sweaters, if you have it–my understanding is that the mill that produced this yarn closed, so the yarn had to be discontinued.)
If you want the sweater to add a layer of warmth, but plan to layer it under a jacket or shell, you don’t need a knitted fabric that provides windbreaking functionality so much as you want a knitted fabric that traps air. These functions aren’t mutually exclusive, but not all insulating fabrics will stop wind. Certain fibers or yarn types trap more air within the strands and between the stitches, providing you with insulation. (Alpaca is known for this, and it is often recommended that you not knit it tightly; otherwise, it won’t trap air as effectively. I haven’t experimented with this so I can’t verify this wisdom.) Yarn types that may provide this functionality include boucles and similarly slightly fuzzy, textured yarns, yarns with a halo of fiber radiating from the component strands or core, yarns that are not tightly spun or plied, and wool yarns that are woolen-spun rather than worsted-spun, although this depends on how tightly you knit the yarn. I can’t give specific examples of substitutes because I don’t really like many fuzzy or halo yarns.
If you want to be able to wear the sweater inside comfortably, you don’t want to roast and you want to be able to lounge around comfortably; I’d suggest a yarn that knits up to a more flexible fabric, and not a dense (i.e. windbreaking) fabric. You might also consider Araucania Nature Cotton, discussed below.
Also think about how you plan to make the sweater fit. Banff was intended to be very loose and lazy, but on some knitters, it’s not massively oversized. Big Sack was designed to have the same fit as Banff, but this was altered by the pattern editor so now it’s loose-fitting, but not hugely loose-fitting. The closer the fit (say, within 6″ of your actual chest measurement), maybe the less dense the fabric should be. If it’s incredibly loose fitting, then a densely knit fabric is okay. Less dense means more flexibility in the fabric, and more ability to conform to your body shape. Really, everybody looks fat in close-fitting chunky knits. Oh, right, fashion models. Everybody normal looks fat in close-fitting chunky knits.
If you don’t want wool or a wool blend:
As I told people when these patterns were released, cotton yarns that knit to this gauge are often quite heavy, and it won’t be pleasant to wear a big garment knit in most pure cotton yarns that knit to a gauge of 14 sts over 4 inches. There are a number of cotton-acrylic blends on the market that will be more comfortable to carry on your frame than pure cotton. The downside to those blends is that they’re often sold in 50g balls, which works out to about 60 meters. That pretty much doubles the number of ends you’ll have to weave in, compared to wool yarns sold in 100g skeins.
However, since both patterns were published, Araucania Nature Cotton has been introduced. Araucania can knit to the right gauge, although I personally prefer it at 4 sts to the inch (and beware the yardage printed on the label–it’s way off) and is comparatively lightweight and very soft. This means it will be more prone to pilling and wear than other cotton yarns, but otherwise I consider it a great alternative to wool for these designs. I hate knitting with cotton, yet I’ve got some in my stash right now.
Edit: I should add (I knew this, but I forgot)–Araucania (that brand, at least) may not be available or easily obtainable in North America for much longer.