Rib is a single-knit fabric with raised vertical ribs and heaps of crosswise stretch, best for cuffs, necklines and fitted trims. Interlock is a double-knit fabric that’s smooth on both sides, thicker and more stable, best for T-shirts, dresses and babywear. Whichever you choose, pre-wash your cotton first: even quality interlock can shrink a little on that first wash, a detail that careful brands factor into every cut, and one that Australian care labelling under AS/NZS 1957:1998 exists partly to help you manage.
TL;DR:
- Pre-washing both rib and interlock fabrics is essential because manufacturing tension can cause significant shrinkage on the first wash, affecting fit and pattern accuracy.
- Rib knit thrives in cuffs and neckbands due to its crosswise stretch and recovery, while interlock’s stability makes it better suited for main garment panels like T-shirts and dresses.
- Higher-quality cotton, such as combed or long-staple, significantly enhances fabric durability and reduces pilling, regardless of knit structure.
- Choosing organic cotton with gentle finishing improves softness and lifespan, with fabric weight and fibre quality being more impactful than knit type alone.
Table of Contents
- How the knits are constructed and how to recognise them
- Property comparison: stretch, weight, durability and wash behaviour
- Sewing and care tips for rib and interlock cotton
- When to pick rib vs interlock: rules of thumb for real projects
- Author and brand perspective: hands-on notes from Baby Goes Retro
- How fibre quality and cotton type change the way rib and interlock perform
- Cost comparison between rib and interlock cotton fabrics
- Environmental impact considerations of producing rib vs. interlock cotton fabrics
- What actually matters when you’re choosing a cotton knit
- Products that put these fabrics to work
- Sources
- FAQ
How the knits are constructed and how to recognise them
Both fabrics start as cotton yarn looped into stitches on a knitting machine, but the loop pattern changes everything about how the fabric behaves. Rib knit alternates knit stitches and purl stitches in a set sequence (1x1, 2x2 and so on), and that alternation pulls the fabric into visible vertical ridges called wales. Interlock knit uses two sets of needles working two separate rib fabrics and locking them together face to face, so you get a double thickness with a flat, identical surface on the front and back.
You don’t need a lab to tell them apart. A few checks do the job:
- Edge curl test: cut a small square and leave the edges free. Interlock lies flat, while a single jersey curls at the edges (rib resists curling too, but shows obvious ribs).
- Both-sides check: run your fingers over front and back. Interlock feels identical on both sides; rib shows clear ridges you can feel and see.
- Stretch direction: pull the fabric side to side. Rib stretches noticeably more than interlock in this direction, which is exactly why it suits cuffs and neckbands.
- Hold to light: thinner rib often lets more light through than dense interlock, a rough proxy for weight before you check the GSM label.
Two terms worth knowing: a wale is a vertical column of stitches, and a course is a horizontal row. GSM (grams per square metre) tells you how heavy the fabric is, which matters for opacity, warmth and how it drapes on a pattern.
Property comparison: stretch, weight, durability and wash behaviour
The two knits diverge most clearly on the numbers, and those numbers should drive your fabric choice more than appearance alone. Rib knit typically recovers 75-85% of its stretch, while interlock recovers 85-95%, though blends with elastane push both figures higher. Weight follows a similar pattern: rib commonly sits at 180-280 GSM against interlock’s 220-350 GSM, so interlock reads heavier, more opaque and warmer on the body.
A controlled comparison of 1x1 rib and plain interlock made from the same yarn found interlock weighed in at 185.86 GSM against rib’s 130.12 GSM, roughly 43% heavier, and recorded a bursting strength of 694.75kPa for interlock versus 391kPa for rib. That gap in bursting strength explains why interlock holds up better under repeated stretching and washing, which is a big reason it turns up so often in babywear that gets washed daily.
| Property | Rib knit | Interlock knit |
|---|---|---|
| Structure | Single knit, alternating knit and purl | Double knit, two ribs locked face to face |
| Stretch recovery | 75-85% | 85-95% |
| Typical GSM | 180-280 | 220-350 |
| Bursting strength (sample study) | moderate | higher |
| Shrinkage (sample study) | noticeable | somewhat more noticeable |
That same study recorded higher shrinkage for interlock than rib in its sample, which is the opposite of what many sewists assume. The lesson holds either way: pre-wash both fabrics before cutting, because manufacturing tension in cotton knits can release on the first wash and throw your pattern out by a few percent if you skip the step.
Sewing and care tips for rib and interlock cotton
Getting a clean result from either fabric comes down to needle choice, seam finish and a bit of patience with shrinkage. Follow these steps and you’ll avoid the most common home-sewing mistakes:
- Fit a ballpoint or jersey needle before you start. A sharp needle designed for wovens will pierce and snag the knit’s loops instead of sliding between them.
- Choose a stretch stitch or narrow zigzag on a domestic machine, or switch to an overlocker for seams that need to move with the fabric.
- Pre-wash and dry your fabric the way you’ll wash the finished garment, then re-measure your pattern pieces before cutting.
- Stabilise necklines and cuffs with a strip of clear elastic or a light knit interfacing, especially on rib, which stretches more than it should but sometimes holds.
- Hem with a twin needle or coverstitch rather than a straight stitch, so the seam stretches instead of popping.
Pro Tip: If you’re using rib for cuffs or a neckband, blend in 5-10% spandex where you can source it: it holds shape through far more wash cycles than pure cotton rib.
For a deeper look at washing routines that protect natural fibres, our guide on washing organic cotton covers temperature and drying settings in more detail.
When to pick rib vs interlock: rules of thumb for real projects
The decision usually comes down to one question: does this part of the garment need to stretch and snap back, or does it need to sit still and look neat? Cuffs, neckbands and waistbands want rib’s crosswise stretch and recovery. Bodices, T-shirts, dresses and most babywear want interlock’s stability and opacity.
- Baby bodysuits and rompers: interlock’s density means less see-through fabric and a smoother finish against sensitive skin.
- T-shirt necklines and sleeve cuffs: rib snaps back into shape after being pulled over a head or hand, which interlock doesn’t do as well.
- Dresses and playsuits: interlock’s weight gives cleaner drape without the fabric clinging.
- Waistbands on dungarees or leggings: rib’s stretch handles movement without losing its shape.
Many baby ranges default to interlock partly because organic cotton finishes tend to sit well on a denser knit, holding colour and softness through the wash cycles that babywear goes through. If you’re adapting a pattern from one knit to the other, widen seam allowances slightly for rib’s extra stretch and expect interlock to need a touch more ease across the chest for the same fit.
Author and brand perspective: hands-on notes from Baby Goes Retro
Daniel has written on fabric care and the rib versus jersey question on the Baby Goes Retro blog, including a practical comparison for baby clothing and notes on organic cotton finishes. The selection approach favours organic cotton with gentle finishing, which influences the preference for interlock in babywear for its stability and softness against skin.
How fibre quality and cotton type change the way rib and interlock perform
The knit structure sets the baseline, but the cotton itself decides how that structure actually feels and lasts. Combed cotton has had its shorter fibres removed before spinning, leaving a smoother, more even yarn that knits into a fabric with fewer stray fibres and less pilling over time. Carded cotton skips that step, so it’s cheaper to produce but tends to feel slightly rougher and pill sooner, a difference that shows up faster on interlock’s dense double face than on looser rib.
Organic cotton doesn’t change the knit structure at all, rib is still rib and interlock is still interlock, but it does affect finishing. Organic fibre is typically processed with fewer harsh dyes and treatments, and Australian product safety guidance points out that finishing and labelling matter as much as fibre choice when you’re picking cotton knits for a baby’s skin. A gentle finish on either rib or interlock will feel noticeably softer than a harshly treated version of the same knit.
Staple length matters too. Longer-staple cotton, often used in combed yarns, produces a stronger, smoother thread that resists the loose, fuzzy pilling you sometimes see on cheaper carded rib after a few months of wear. If you’re choosing between two fabrics with identical GSM, the one spun from better-quality cotton will usually outlast the other, regardless of whether it’s rib or interlock.
Cost comparison between rib and interlock cotton fabrics
Interlock generally costs more per metre than rib, and the reason sits in the machine, not the cotton. Producing a double-knit fabric on an interlock machine uses two sets of needles and more yarn per square metre than a single-knit rib machine, so the extra material and machine time show up in the price you pay at the fabric counter.
Rib’s lower cost makes it the practical choice for small trim pieces like cuffs, neckbands and waistbands, where you only need a small quantity and the stretch matters more than the weight. Interlock’s higher price is easier to justify on garments where you’re cutting large pattern pieces, such as a T-shirt body or a baby romper, because its extra bursting strength and stability translate into a garment that holds its shape for longer.
Blended fabrics, particularly rib with a small percentage of spandex, sit at a premium over plain cotton rib because the added fibre improves long-term recovery. If you’re stitching a one-off garment, that premium is often worth paying for a neckband or cuff that still looks new after dozens of washes. For bulk or budget projects, plain cotton rib remains the cheaper, perfectly serviceable option for trims, while interlock is worth the extra spend wherever the fabric is the main body of the garment.
Environmental impact considerations of producing rib vs. interlock cotton fabrics
Growing and processing the cotton itself carries the bulk of the environmental load for either knit, and that load doesn’t change much based on stitch structure. Where the two fabrics start to differ is in the amount of raw cotton needed per garment: interlock’s higher GSM means more fibre goes into the same size piece of fabric compared with lighter rib.
Knitting interlock also takes more machine time and yarn feed than knitting an equivalent length of rib, which adds slightly to the energy used at the mill stage. Neither difference is large enough to make one knit clearly “greener” than the other on its own, and the more meaningful environmental choices sit further upstream, in how the cotton is grown, dyed and finished, rather than in which knit structure it ends up in.
Choosing organic cotton, in either rib or interlock, generally means fewer synthetic pesticides and less chemical-heavy processing during growing and finishing. That’s a bigger lever on environmental impact than the knit type itself, which is why the finishing and fibre sourcing behind a fabric matter at least as much as whether it’s rib or interlock when you’re weighing up the full picture.
What actually matters when you’re choosing a cotton knit
The conventional advice, “rib for stretch, interlock for stability”, is true but it undersells how much fibre quality and finishing decide whether a garment feels good after the tenth wash, not just the first. Two fabrics with identical GSM and the same knit structure can behave completely differently depending on whether the cotton was combed or carded, and how gently it was dyed.
If I had to prioritise one thing for a maker or a parent, it’s this: check the fibre quality and finishing before you worry about knit structure. Stretch recovery numbers and GSM ranges are useful shortcuts, but they’re averages from samples, not guarantees for the specific bolt or garment in front of you. Pre-washing is the cheapest insurance available and the step most home sewists skip.
Rib and interlock aren’t competing fabrics so much as different tools for different jobs on the same garment. The mistake isn’t picking the “wrong” one, it’s assuming either fabric will perform to its typical numbers regardless of how it was grown, spun and finished.
— Daniel
Products that put these fabrics to work
Once you know what to look for, shopping gets a lot simpler. The Kite Pig Pannage Long Sleeve Bodysuit uses a stable, opaque knit that suits the daily wash cycles babywear goes through, while the Frugi Rainbow Print Bodysuits (4-pack) and Frugi Fun Flowers Bodysuits (2-pack) give you ready-made layers without any cutting or sewing at all.
For playwear that needs a bit more movement, the Blade & Rose Honey Bee Romper and the DUNS Sweden Clover Playsuit pair stable bodies with stretchier trims where they’re needed.
- Browse the full baby clothes collection for more bodysuits, rompers and dungarees.
- All orders ship for a flat $7.95, free over $97, with 30-day easy returns and exchanges.
- Every piece is organic cotton from ethically produced European brands, chosen for softness on sensitive skin.
Sources
- Rib knit and interlock: how they differ from standard jersey - TextileTuts
- Comparative analysis of physical properties of 1 × 1 rib and plain interlock fabrics
- MSTGN2013 - Identify fibres, yarns, fabrics and textile materials
FAQ
What is the difference between rib and interlock fabric?
Rib is a single-knit fabric with alternating knit and purl stitches that form visible vertical ribs and strong crosswise stretch. Interlock is a double-knit fabric made from two interlocked rib layers, giving a smooth, identical surface on both sides with less stretch but more stability and weight.
Is interlock cotton good for babywear?
Interlock cotton is a solid choice for babywear because its density gives good opacity and holds up well to the frequent washing that baby clothes need. Its higher bursting strength compared with rib means it resists wear better under repeated stretching and laundering.
Is cotton rib fabric good or bad?
Cotton rib is neither good nor bad on its own, it’s suited to specific jobs like cuffs, neckbands and waistbands where crosswise stretch and recovery matter most. Its stretch recovery of 75-85% is lower than interlock’s, so it isn’t the best pick for a garment’s main body where stability matters more.
What fabrics should sewists be cautious with?
Any knit fabric with unclear fibre content or care labelling is worth approaching carefully, since finishing and fibre quality affect comfort and durability as much as knit structure. Checking care labelling under Australian standards before buying or cutting into a fabric helps avoid surprises after the first wash.
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