What type of glass is the most eco-friendly?
As mentioned in where glass comes from, it’s impossible to trace back through the supply chain and figure out ethical and sustainable sourcing. Generally speaking, annealed glass will have a lower energy use. Purchasing locally from a supplier who purchases from a local fabricator will reduce fuel use for transportation, but honestly that has very little impact overall. It is a good idea to purchase direct from a contractor rather than a retailer to avoid unnecessary packaging.
As is true of any attempts at conscientious consumption, reduce is the guiding principle. Buy less. That is followed by reuse. Salvaged materials will be significantly greener than new, but probably not cheaper. If you can reduce or reuse that will always be superior to any other choices available to consumers.
If you must purchase new, consider getting products that will last the longest, have a timeless quality and require the least maintenance. Also factor in energy efficiency in the case of windows.
In truth, when it comes to choosing a glazier(glass contractor), eco-friendliness shouldn't carry much weight in deciding who to work with. We are all subject to the same constraints of local suppliers and recycling availability.