How do canned soup companies keep their noodles from absorbing all the liquid in the can? I like to make noodle soups. Chicken noodle, pho, k'tieu, soba, and so on; there are many different types of noodle involved. In every case, if the soup goes into the fridge, the noodles absorb all the broth fairly quickly. Typical fixes for this include:


cook the noodles separately and add to the soup when serving;
freeze the leftovers;
eat all the soup right away!


But when I buy canned soup from the grocery store, the noodles are never blown up and they don't seem to blow up even after opening the can and leaving summer in the fridge.

What is the secret? Is it a special kind of noodle, something about the broth or a heavy duty industrial preservative at work?
Canning
I've been looking up canning, as I suspected it had much to do with the process of noodles not absorbing all the water. I've found this tangentially related post and quoting:

You CAN can pasta yourself. It is not difficult but, like the commercial caners [sic] you will need to make sure it is high acid (they add flavorless citric acid) but using a red tomato sauce works just as well.

I have also found this very interesting set of ideas:

The idea is simple and genius: combine par-cooked noodles, a bit of vegetable base, some raw sliced veggies, and a few seasonings inside a jar.

Partial cooking
On an article about partial cooking which has some good ideas on par-cooking. I suspect this, combined with the above factors, as well as vacuum-sealed canning, is what allows for noodles, and vegetables/potatoes, to not absorb all the liquid.
Dig deeper
If you wish to dig deeper, I have found a scientific paper by American Association of Cereal Chemists specifically on the topic of liquid absorption by noodles:
Noodles. V. Determination of Optimum Water Absorption of Flour to Prepare Oriental Noodles