Clarification needed about english expression

[nunogit]

In "Pandemic" where you read "flat surface" what does that mean?

The query doesn't seem to reflect the flatness of the surface. Only surfaces in general.
This expression has lead to somehow questionable translations in Portuguese, where flat can be ambiguous (flat, without wrinkles or folds, or flat as in plane, like a table top)

[egonw]

Good question. I would need to go back to the relevant literature. I remember that some services, like metal surfaces, it attached better to than others. So, intuitively, I'd say both.

[nunogit]

I remember a study with different materials. Things like copper were tested.
I don't remember anything particular about their properties (flatness?). Maybe leaving the "flat" out is a good idea.