These disc brake pads come in two types of compound: Organic (BBS-441) and Sintered (BBS-441S).
BBB-441, compatible with: Sram Level, Level T/TL , Avid Elixir, SRAM XX / XO and Avid DB and Elixir series. Trickstuff C21 compatible. Organic
BBS-441S compatible with: Sram Level, Level T/TL , Avid Elixir, SRAM XX / XO and Avid DB and Elixir series. Trickstuff C21 compatible. Sintered (metal)