I love milk bags. I can dump them in the fridge drawer and they take up hardly any space, they don't weigh ten pounds each like 4L jugs, when empty they have a volume of zero, unlike 4L jugs, and they are way easier to pour. The only downside is they are not recyclable, but it's such a small volume of plastic I don't think it really matters.
WestSoy is one major soymilk producer that uses Tetrapak. In stores like Sprouts and Trader Joe's it's often the only soymilk available. Tetrapak is nice in that it doesn't need to be refrigerated until you open it, but it's made of paper with a layer of foil underneath it cannot be recycled.
Tetrapak can be recycled, though depending on where you live it may or may not actually be recycled. It's certainly more involved than recycling, say, glass.
https://productxplorer.tetrapak.com/packaging/package/tetra-...
That's basically all I've ever seen. Cardboard + plastic spout. From what I can tell, they are recyclable.
https://earth911.com/home-garden/recycling-mystery-milk-and-...