That question^^
I didn’t find anything searching www.howstuffworks.com, and I didn’t find anything here, so any help would be nice
I visited the Engineered Fabrics plant in Rockmart GA a few years back. They manufacture bladder style fuel tanks for military A/C.
Here’s how they were making them then.
There are two layers of cured (vulcanized) rubberized fabric that make up the tank. In between these layers are a layer of uncured (non-vulcanized) rubber. The vulcanized rubber is unaffected by jet fuel. If there is a penetration of the tank by an object, such as shrapnel from a cannon shell or missle warhead, the fuel flows through the hole and hits the unvulcanized rubber between the two layers. This rubber swells due to the fuel and plugs or at least greatly reduces the size of the hole.
I visited the plant about 9 years ago, so there may be other techniques in use now. But that’s what they used then.
Additional information I found interesting about fuel tank manufacture at no extra charge:
The tanks are layed up by hand over cardboard forms. Basically a cardboard box. After the tank has been manufactured you might wonder how thay get the form out? they fill the tank with water and the cardboard softens. Then someone reaches in through an opening and pulls out the cardboard.
Some tanks are built up over a plaster mold if the shape is too complicated for cardboard. Again after the tank has been manufactured, water is added and the tank is beat with rubber hammers to break up the plaster mould. Then the parts are removed through one of the access holes.