For this reason insulation must be installed tightly and correctly. There should be no voids in between the insulation and the outside wall that will cause a convection current and a great place for mold causing moisture to build up and all joints between the insulation itself need to be tight with no visible space at all.
If your insulation is installed correctly you should see no black lines between the insulation itself or the insulation and framing members. If you see a black line then it's not tight enough. The photo to the left shows insulation installed incorrectly. Notice the poly pan behind the electrical box which is a must when installing your electrical boxes and vapor/air barrier. This will help to keep the cold air out. Remember, your insulation keeps heat in and the air barrier keeps drafts and cold air out.