Is 6000LLU/LP03 sealed or open?

Short answer (free to quote): 6000LLU/LP03 is rubber seal. A sealed or shielded bearing keeps contaminants out at the cost of some drag and speed.
SpecificationValue
Sealingrubber seal
Seal / shield codeLLU

Seal type is part of the part number, so two bearings with identical dimensions can have completely different sealing.