Is < 0.04 Ω the same as 80 dB shielding?
No. Surface resistance and shielding effectiveness measure different properties.
Why can similar resistance give different shielding?
Construction, plating quality, thickness, frequency and test geometry can all affect shielding.
When is low resistance especially important?
When the fabric must make conductive contact across seams, gaskets, grounding interfaces or laminated structures.
Project note: Use supplier data as a starting point. Validate the finished assembly at the relevant frequencies and environmental conditions.