There's a debate going on in the packaging world regarding whether glass or plastic is the better "Green" option. Not just plastic but PET. PET is wholeheartedly competing for glass business touting, "Anything you can do, I can do better"!
For a long time glass has been considered to be the better enviro-choice for your packaging options. Glass is made from sand and can be recycled infinitely without affecting the quality of the product. It's been in the recycling stream for ages and can be recycled and made into another bottle again. Same as it was before. What people don't realize is that there are few glass manufacturing facilities in the U.S. and therefore it will likely not be made into a bottle again. A good reason for this is even if a glass facility would like to purchase said recycled glass material, it is very heavy and uses much fuel to transport, oftentimes, defeating the purpose of sustainability.
PET on the other hand is very lightweight and therefore uses much less fuel to transport. PET is just as common in the recycling stream and as of recently can also be purified to be suitable for food contact once again. PET is offered in as many if not in more colors than glass and is more cost effective. While glass is not a suitable choice for many bathroom packages as it can shatter and pose a risk for injury, PET is nearly shatterproof and therefore is the safer option for the consumer and reduces loss for the manufacturer. Though improvements are being made, PET will still break down and lose quality as it repeats its round in the recycling stream and must be downcycled. For instance, what was once a milk bottle is now a plastic park bench. There are also barrier issues when it comes to plastic. Some products can permeate or break down the plastic and PET will melt at high temperatures, making it useless for many sauces and juices that are hot-filled. There are some Hot-Fill PET offerings, but options are limited and minimums are high.
Many foods simply taste better from glass.
So what have we learned today? Clearly, there's no definite answer here and it seems to be entirely situational. What is good in glass is not always good in plastic so perhaps they'll both always have their moment to shine.