We may not light with any product of a tree, except flax. And no tree-product can contract tumah-contamination from sheltering [a contaminated object], except flax. A wick made from a cloth that one twisted but did not singe — R’ Eliezer says: It is susceptible to tumah-contamination, and we may not light with it. R’ Akiva says: It is not susceptible to tumah-contamination, and we may light with it.