I argue that the concept of an epistemic interface is a useful one to add to the epistemic ecology toolkit in order to enrich our investigations concerning the complex epistemic phenomena arising on social media. An epistemic interface is defined as any informational interface (be it technical, human or institutional) that facilitates the transfer of epistemic goods from one epistemic environment to its outside, be that another epistemic environment or a person. When assessing the kinds of epistemic environments emerging on (...) social media platforms, we should not only look at their epistemic health or hostility as environments, but also look at how these environments interact with each other, at their interfacing. I show that several epistemic problems specific to social media such as epistemic bubbles, echo chambers and epistemic flooding can be understood also in terms of faulty epistemic interfacing, which adds a layer of complexity to the discussion. The paper proposes two criteria for healthy epistemic interfacing: preserving the flourishing of epistemic agents, and preserving in some form the value of epistemic outcomes as these cross the environment to the outside world. These criteria should give rise to specific norms and design requirements for healthy interfacing, but such norms will need more empirical work before these get formulated. (shrink)