J / kg ▁of ▁lat ent ▁heat , ▁as ▁against ▁a ▁specific ▁heat ▁capacity ▁of ▁around ▁one ▁k J / kg . ° C ▁( that ▁is ▁per ▁degree ▁Cel si us ) ▁for ▁m ason ry . ▁ ▁The ▁storage ▁density ▁can ▁therefore ▁be ▁ 2 0 0 ▁times ▁greater ▁or ▁more ▁than ▁m ason ry ▁per ▁kg ▁if ▁an ▁exact ▁temperature ▁is ▁required . ▁ ▁If ▁a ▁temperature ▁variance ▁of , ▁say , ▁ 4 ° C ▁can ▁be ▁allowed , ▁the ▁density ▁is ▁ 5 0 ▁times ▁greater . ▁▁ ▁The ▁specific ▁heat ▁capacity ▁of ▁water ▁is ▁much ▁higher ▁at ▁ 4 . 2 , ▁so ▁the ▁storage ▁density ▁of ▁the ▁pos ited ▁PC M ▁ranges ▁between ▁ 5 0 ▁and ▁ 1 2 . 5 ▁times ▁that ▁of ▁water . ▁ ▁Organ ic ▁PC M s ▁ ▁H ydro car b ons , ▁primarily ▁para ff ins ▁( C n H 2 n + 2 ) ▁and ▁lip ids ▁but ▁also ▁one ▁sugar ▁alco hol . ▁▁ ▁Adv antages ▁ ▁Free ze ▁without ▁much ▁super co ol ing ▁ ▁Ab ility ▁to ▁m elt ▁con gru ently ▁ ▁Self ▁nucle ating ▁properties ▁ ▁Comp at ibility ▁with ▁conventional ▁material ▁of ▁construction ▁ ▁No ▁seg reg ation ▁ ▁Chem ically ▁stable ▁ ▁Sa fe ▁and ▁non - re active ▁ ▁Dis adv antages ▁ ▁Low ▁thermal ▁conduct ivity ▁in ▁their ▁solid ▁state . ▁High ▁heat ▁transfer ▁rates ▁are ▁required ▁during ▁the ▁free zing ▁cycle . ▁N ano ▁compos ites ▁were