Most products have qualities that are "green". Spray Foam Insulation products all have one very important green factor in common and that is energy savings. SPF can reduce your energy use for heating and air conditioning by up to 20% which is incredibly green. Using SPF products greatly reduces the amount of electricity and fuels you will need which equates to less greenhouse gasses due to the production of these resources.
Some SPFs are also made using renewable resources from natural oils like soybean or castor oil. These oils only make up a part of the actual foam though so only a part of the end product is bio-based.
When it comes to insulation products the most important factor to look at is the R-value. The R-value is used to measure a product's resistance to heat flow.
If the value is high then the product is a good insulator. The FTC (Federal Trade Commission) provides guidance for understand R-values in their consumer alert Home Insulation Basics:
Higher R-Values = Higher Insulating Values.