Envelope lining 7

This is the lining of a fairly large envelope posted in the UK in early 2019. It is a simple pattern of blue lines, in a hexagonal shape.

Envelope lining 6

This particular envelope comes from the UK. It came from the same set of materials as "Envelope Lining 5"-- a set of leaflets for the UK Charity Prostate Cancer UK , encouraging donations. This was the envelope the charity provided for donors to send in their donations.

The pattern of this envelope is a "herring-bone" pattern in blue. 

Envelope lining- 2

Here is another lining of a recent envelope, which was sent from the United Kingdom

Much like the previous examples, the pattern used is formed from fine lines. However, the pattern used here appears to be more complicated than the previous examples.

Envelope linings 1

This pattern forms the lining of a recent envelope. The design is a fairly simple ( but finely engraved) pattern of wavy lines, not unlike Guilloche.

The pattern , strictly speaking, is not a separate piece of paper pasted onto the inside of the envelope, but is rather printed directly on the inside of the envelope itself.

As you can see, from the above image, this pattern also comes in a black/grey colour.
This is one of the more common patterns. I have seen at least a dozen envelopes lined with this paper.