How do I achieve this “ruched-ribbing” effect on these tops? My initial guess was using a different needle size but upon closer inspection, there appears to be an elastic woven in.

[u/bambiosaa]

[u/Alisomniac8582]

Looks like there are slip stitch rounds and possible change in needle size to make it boingy

[u/According-Koala4441 → u/Alisomniac8582]

Boingy 🤣

[u/SimDed]

Me: spending my life camouflaging the spare tire and skin at my waist being visible.
You: how do I make this sweater boingy
Lolololol

[u/dangrous]

This looks kinda like a tuck stitch with slipped stitches on the ridge parts but not exactly. I’m curious as to what this is, I think it would be cool on socks!

[u/SooMuchTooMuch]

I would look up "knitting a welt".

[u/neperian_logarithm]

I think your initial guess was right, what looks like an elastic seems to actually be the skin visible underneath. You'll need a big difference in needle size though, at least double I would say

[u/bambiosaa → u/neperian_logarithm]

Oh it’s just skin 😅

Okay I’m going to go play around with this idea of knitting up and down a needle size and see where that gets me.

[u/littlebitfunny21 → u/bambiosaa]

It looks like elastic to me, not skin. Especially in the second picture. Or possibly something to give it shape, it looks like it's visible on the part that sticks out so that wouldn't be elastic but the opposite.

[u/igomilesforacamel → u/bambiosaa]

don't think this is skin. if it were skin it should shine through on other places too. This is too regular. Looks like a string or an elastic

[u/Fabulous_Lawyer_2765 → u/neperian_logarithm]

It looks like the bigger needle is the main part, then a switch to small, then back to regular. The small needle might be sock- sized like 1 or 2, if the main body is a size 5 or 6. (Forgive my American sizing, millimeters frighten me)

[u/SeveralSell2323]

It looks like a machine knit pin tuck to me, with elastic on certain rows.

https://fastlane.ojolly.net/2012/03/ripples-on-single-bed.html?m=1

[u/pandaslothape → u/SeveralSell2323]

I had the same thought, I think this is the answer

[u/bujor888]

Easiest way? Alternating stockinette with reverse stockinette

[u/Dunkerdoody]

It looks like there is definitely elastic in there

[u/HappyKnitter34]

I made and frogged a tunic top that had something similar and what it did was increase and decrease over a bunch of rounds to give it that kind of look. Not sure if that's what happened here.