PETG is short for Polyethylene Terephthalate. It is a very durable material and is generally considered impact-resistant. It is also lightweight and has a small amount of flexibility. It can handle higher temperatures than PLA. Due to these factors, it has been gaining in popularity. It is a good all-around material and is also available in a variety of colours.
Many find that 3D printing with PETG can be difficult when you begin using it, but once you find the correct settings you will find it is quite easy to use and produces high quality products.