Someone above said the air is thicker. I'm not sure if that is true. I always felt like humid days were the worst for air resistance. But I would not be surprised to learn that colder air is more difficult to breathe efficiently.
[TABLE]
[TR]
[TD="colspan: 4"]Effect of temperature on properties of air
[/TD]
[/TR]
[TR]
[TD]
Temperature
T (°C)
[/TD]
[TD]
Speed of sound
c (m/s)
[/TD]
[TD]
Density of air
ρ (kg/m[SUP]3[/SUP])
[/TD]
[TD]
Characteristic specific acoustic impedance
z[SUB]0[/SUB] (Pa·s/m)
[/TD]
[/TR]
[TR]
[TD]35
[/TD]
[TD]351.88
[/TD]
[TD]1.1455
[/TD]
[TD]403.2
[/TD]
[/TR]
[TR]
[TD]30
[/TD]
[TD]349.02
[/TD]
[TD]1.1644
[/TD]
[TD]406.5
[/TD]
[/TR]
[TR]
[TD]25
[/TD]
[TD]346.13
[/TD]
[TD]1.1839
[/TD]
[TD]409.4
[/TD]
[/TR]
[TR]
[TD]20
[/TD]
[TD]343.21
[/TD]
[TD]1.2041
[/TD]
[TD]413.3
[/TD]
[/TR]
[TR]
[TD]15
[/TD]
[TD]340.27
[/TD]
[TD]1.2250
[/TD]
[TD]416.9
[/TD]
[/TR]
[TR]
[TD]10
[/TD]
[TD]337.31
[/TD]
[TD]1.2466
[/TD]
[TD]420.5
[/TD]
[/TR]
[TR]
[TD]5
[/TD]
[TD]334.32
[/TD]
[TD]1.2690
[/TD]
[TD]424.3
[/TD]
[/TR]
[TR]
[TD]0
[/TD]
[TD]331.30
[/TD]
[TD]1.2922
[/TD]
[TD]428.0
[/TD]
[/TR]
[TR]
[TD]−5
[/TD]
[TD]328.25
[/TD]
[TD]1.3163
[/TD]
[TD]432.1
[/TD]
[/TR]
[TR]
[TD]−10
[/TD]
[TD]325.18
[/TD]
[TD]1.3413
[/TD]
[TD]436.1
[/TD]
[/TR]
[TR]
[TD]−15
[/TD]
[TD]322.07
[/TD]
[TD]1.3673
[/TD]
[TD]440.3
[/TD]
[/TR]
[TR]
[TD]−20
[/TD]
[TD]318.94
[/TD]
[TD]1.3943
[/TD]
[TD]444.6
[/TD]
[/TR]
[TR]
[TD]−25
[/TD]
[TD]315.77
[/TD]
[TD]1.4224
[/TD]
[TD]449.1
[/TD]
[/TR]
[/TABLE]