Tyvek ntawv lub hnab ntim txias yog siv cov khoom siv hauv ib puag ncig, uas zoo ib yam li cov khoom lag luam yas, tuaj yeem muab ntxuav dua, thiab tiv taus kua muag. Qhov tseem ceeb tshaj plaws yog cov khoom siv yog eco tus phooj ywg, yog li nws rov siv dua.