A material for nonmagical but still highly useful items in Nethack. The oilskin cloak, aka slippery cloak, provides good magic cancellation and protects from the grab attacks of such monsters as owlbears and eels. The oilskin sack protects all the objects contained within it from being damaged by the elements: e.g., the sack can be safely submerged without rusting weapons or armor in it, and fire traps will not burn spellbooks or scrolls, or boil potions, contained in the sack. A common practice is to nest a bag of holding inside an oilskin sack for increased carrying capacity as well as waterproofing.