For baking, use food-grade silicone, typically indicated on the manufacturer's labeling. These silicones are heat-safe up to 400°F/205°C. These is my Ube Velvet cake recipe baked in silicone molds to create 4-inch mini cake layers. Silicone is flexible, which is pretty different than other metal-based baking pans you may be used to.
Step 1. Prepare the mold. Spray the molds with some cooking oil. Place your molds on a baking sheet BEFORE filling. (Moving an unsupported silicone mold filled batter is a recipe for disaster.) The metal tray also helps transfer heat to the bottom of the mold while in the oven. Step 2. Scoop the prepared cake batter into the mold.
Make sure to check that it fits your model of the Instant Pot. Bonus, you can also use these silicone molds in the oven. Perfectly cooked Mediterranean-style Instant Pot egg bites with red peppers, sun-dried tomatoes, and feta cheese.
The mold I use to make my mini cakes creates perfectly flat 4-inch (in diameter) layers that are a little less than an inch tall. There are 6 holes (or "cavities" as the mold industry refers to them), and each holds about 2 cupcakes worth of batter. I buy mine from Amazon, which you can see here if you like.