If the two people are using the 40° blankets side by side snapped together, the estimated temperature would still be 40° because the insulation loft has not increased. However, there will be considerably more heat created and thus retained when considering two body masses, so pending the individual bodies and the thermodynamics associated with each (calorie intake, body mass, etc.), it is highly plausible that the couple or pair could take the two Puffle's down to lower temperatures - such as 32°F.