John XXIII was splendidly embalmed, as can be noted by the condition of his body currently on display in a glass case in St. Peter's. Paul VI was horridly embalmed. JPI was embalmed; JPII wasn't.
Pius XII was "embalmed" by his quack doctor (who likely caused his death) who actually only rubbed some oil over his body and dusted his face with powder.
Pius XII lay in state for eight days in humid October weather. Swiss Guards had to take fifteen minute turns due to the odor and several cardinals were overcome with nausea when praying next to the bier.
When his body was transferred to the wooden casket for the Mass, his nose literally detached from his face, due to rapid decomposition.
JPII was most definitely embalmed. How do you think he stayed in such good condition for an entire week? He was even touched up during the week.