Cannot be Frozen is an attribute found on some Runewords, Set and Unique items. It is almost an essential attribute to have for melee characters, particularly in Hell difficulty. It prevents the slowing effect of cold attacks from affecting the character, thus allowing that character to continue moving and attacking at their normal speed. This attribute does not, however, affect cold damage, nor does it prevent Holy Freeze or Decrepify from slowing down the character. The latter is because Decrepify is not a cold-based attack and the former is because the designers decided that Holy Freeze would override Cannot be Frozen.

Once affected by chilling, activating the attribute, such as switching to a weapon or shield which possesses it will not override the effect and will have to wait out the chill from that particular attack before the immunity to chilling will work again. So being chilled by a Cold Arrow from a monster, switching to Rhyme and then being hit with a monster level Frost Nova a second later, a character will only have to wait out the Cold Arrow's freeze, not the Frost Nova's duration.