The most common cause of rubbery seitan is overworking the dough. Gluten forms as the dough is kneaded, and adding gluten to a gluten-laden food is a recipe for a spongy, rubbery texture. Avoid kneading the dough too much to maintain a meaty texture.  The transition from one temperature extreme to another can also result in a rubbery texture. Don’t take the seitan out of the pan it’s cooked in right away. Let it sit for at least 15 minutes first. This recipe recommends 20 minutes of resting time before transferring it to the fridge to cool.