Waterproof Casing

[Rick]

I'm about to make this Tongue Head Cheese which calls for the following;

"Stuff into middles or bladders loosely and sew the ends with twine. You may use large diameter waterproof casings.
Poach at 82°C (180°F) for 90-120 min (depending on size) until the internal temperature of the meat reaches 68-70°C (154-158°F). Remove air with a needle from pieces that swim up to the surface."

I'm wondering if a middle or bladder would withstand the 180°F poach? Also they're pretty pricey. Then if you were to sew these closed how does that make it waterproof?
What casing would you suggest I look at that would be waterproof? I've run across what is called a High-Barrier casing which I believe is waterproof, but I have no experience with this type of casing.

So the confusion seems to center around the need for a waterproof casing involved with poaching at 180°F.

[redzed]

If you are referring to using hog middle casings, I would avoid using them for this purpose. They are quite fragile and can be very thin in places. Your head cheese could burst or the broth can leak out during poaching. Bladders on the other hand will work well. They are very strong and you won't need to sew anything, just tie the end. High barrier casings is exactly what you need if you don't want to use natural. I don't know where you buy your casings from, but there are products that are made especially for head cheeses. If using artificial casings don't follow the advice to pierce them while poaching or else the broth will leak out. Natural casings will usually reseal after the air is released, but even then you have to be careful.