▁is ▁to ▁increase ▁thermal ▁conduct ivity ▁by ▁adding ▁a ▁highly ▁conduct ing ▁solid ▁( such ▁as ▁the ▁co pper ▁mesh ) ▁into ▁the ▁relatively ▁low - con duct ing ▁PC M , ▁thus ▁increasing ▁overall ▁or ▁bulk ▁( ther mal ) ▁conduct ivity . ▁If ▁the ▁PC M ▁is ▁required ▁to ▁flow , ▁the ▁solid ▁must ▁be ▁por ous , ▁such ▁as ▁a ▁mesh . ▁ ▁Sol id ▁compos ites ▁such ▁as ▁fi berg lass ▁or ▁ke v lar ▁pre pre g ▁for ▁the ▁a eros pace ▁industry ▁usually ▁refer ▁to ▁a ▁fi ber ▁( the ▁ke v lar ▁or ▁the ▁glass ) ▁and ▁a ▁matrix ▁( the ▁gl ue , ▁which ▁solid ifies ▁to ▁hold ▁fib ers ▁and ▁provide ▁compress ive ▁strength ). ▁A ▁thermal ▁composite ▁is ▁not ▁so ▁clearly ▁defined ▁but ▁could ▁similarly ▁refer ▁to ▁a ▁matrix ▁( sol id ) ▁and ▁the ▁PC M , ▁which ▁is ▁of ▁course ▁usually ▁liquid ▁and / or ▁solid ▁depending ▁on ▁conditions . ▁They ▁are ▁also ▁meant ▁to ▁discover ▁minor ▁elements ▁in ▁the ▁earth . ▁ ▁App lications ▁ ▁App lications ▁of ▁phase ▁change ▁materials ▁include , ▁but ▁are ▁not ▁limited ▁to : ▁▁ ▁Th erm al ▁energy ▁storage ▁ ▁Sol ar ▁cook ing ▁ ▁Cold ▁Energy ▁B atter y ▁ ▁Cond ition ing ▁of ▁buildings , ▁such ▁as ▁' ice - storage ' ▁ ▁C ool ing ▁of ▁heat ▁and ▁elect rical ▁engines ▁ ▁C ool ing : ▁food , ▁be ver ages , ▁coffee , ▁wine , ▁milk ▁products , ▁green ▁houses