Siaair pads use Aluminum Oxide as the abrasive, while Abralon uses silicon Carbide. Their size and foam backing are almost identical. Both use FEPA as their grading so their grit numbers are also identical.
Their main functional difference for use on bowling balls seems to be that Siaair pads last slightly longer than Abralon pads.
Example: for the 4000 grit pad, I'll get 3 - 5 full uses per ball with standard light pressure needed to get as close to a true 4000 grit reading as possible. For the Siaair 4000 grit pads, I'll get 4-6 uses, roughly speaking.
Of course other pads, like 900Global's NEAT and 3m Trizact, the use per pad is significantly higher. (FYI 900G's NEAT pads have been replaced recently by their ICE pads.)