While many recipes call for using either parchment paper or a silicone baking mat like a Silpat [1], the two aren't 100-percent interchangeable. Both use food-grade silicone to keep food from sticking to a surface, but they differ in some crucial areas and should be used accordingly.
A silicone baking mat is much thicker than a sheet of parchment paper and thus insulates the pan it's laid atop. This can be a boon when baking delicate cookies, like these French macarons [2]. On the flip side, use parchment paper if browning on the underside is desired, like when roasting vegetables or baking sugar cookies [3].
Because it is disposable, parchment can be used in many recipes where a silicone baking mat cannot: It can be cut to size to line cake pans and casserole dishes [4]. Additionally, parchment paper can be cut to size and folded into an airtight pouch around delicate items like seafood [5] to cook en papillote.
In most other applications, either nonstick liner can be used; the choice is up to you. Some cooks prefer to use a silicone baking mat, as it is reusable and thus eco-friendly. Others prefer parchment paper for its ease of use (simply recycle a sheet after use instead of scrubbing it clean).
