The outside of padded envelopes, or padded mailers, “can be made of heavy paper, paperboard or corrugated fiberboard.”
These are recyclable materials if they were recycled as a stand-alone item. It’s when they are fused with padding material that their ability to be recycled becomes more difficult to discern.
In 1957 two inventors named Alfred Fielding and Marc Chavannes were attempting to create a three-dimensional plastic wallpaper. Although the idea was a failure, they found that what they did make could be used as packing material.
Now known as “bubble wrap”, this plastic material contains evenly spaced, protruding air-filled pockets. The term “bubble wrap” is a generic trademark owned by Sealed Air Corporation, co-founded by Alfred Fielding in 1960.
The outside of padded envelopes, or padded mailers, “can be made of heavy paper, paperboard or corrugated fiberboard.” 
