rubbered in
adj.— «Regarding this track, us drivers use the term “rubbered in.” This means the track is getting more grip and that is really the case here. This makes it very challenging from a driver perspective but also extremely difficult from an engineering stand point.» —“The Fans in Mexico Are Very Passionate” by Nic Jonsson Grand-Am (Daytona Beach, Florida) Apr. 16, 2008. (source: Double-Tongued Dictionary)
Further reading
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“rubbered in” is the opposite of “green”.
A “green” track has little grip, might have dirt on it, etc. The first drivers who do laps on the track clean the track by sweeping all that debris off the racing line.
Then, the tires start laying down a significant layer of rubber which gives additional grip on the line.
This is quite different than the “marbles” that build up offline, in which hot pieces of tire, shaped like small marbles, fly off and stick to the road. Those offer almost no grip.