If you cover an outdoor houseplant to protect it from frost..?

i was wondering if by covering a plant ' loosely ' in plastic when the temps dip to 36* at night if that plant generates some sort of heat to actually make it warmer in its tent than the actual air temparature ...i have a cactus i like to leave outdoors as long as possible since the days are still quite pleasant..( and he is a bear to move around)....so i cover him on "frosty" nights with a huge plastic bag and uncover him in the AM to let him enjoy the sun.. i was just wondering if the plant can make his heat in his little plastic "tent"...