Hmoov plhaub yog cov hmoov ua los ntawm kev sib tsoo thiab sib tsoo cov plhaub. 95% ntawm nws cov khoom xyaw yog calcium carbonate, chitin, thiab me ntsis ntawm cov amino acids thiab polysaccharides. Nws tuaj yeem siv ua cov khoom siv zoo rau cov khoom noj, tshuaj pleev ib ce thiab kho kom zoo nkauj sab hauv, thiab siv rau hauv cov tsiaj txhu thiab nqaij qaib. Cov khoom noj thiab cov khoom noj uas muaj calcium ntxiv, kev ua cov hniav nyiaj hniav kub, cov tshuaj desiccants, thiab lwm yam.