Colorado Window & Siding, Inc. prefers to use minimum expansion foam on all installations unless the need calls for fiberglass.
Fiberglass works well when the gaps are small and it can be packed into small tight seams. This is because the foam gun tip will not fit and the foam cannot get into the gap to fill it.
Foam ensures a seal that fills all of the nooks and crannies. This minimizes water and air infiltration. Foam products also generally produce higher R-values than fiberglass insulation. However, the company and installer must be experienced at using foam because of some pitfalls of the product.
If not used properly, foam can warp the window frame and void the warranty on your windows. It can also dislodge the interior and exterior trim during installation, If not cleaned quickly it can stain fabrics. All of these warnings are not to scare you but to warn you of potential issues with a company. More and more companies are switching to foam insulation on their installs because of the benefits.
Make sure the company is experienced at what they do and have crews that have a similiar number of years of experience. It does not matter if they are employees or subcontractors, what matters is the years of experience they have. The more years of experience will always produce better results.