I have been trading for the past 20+ years specialising in selling glassine envelopes manufactured exclusively in the UK. They are superb quality products
Bespoke sizes can be made up to a maximum of 127 x 195 ( minimum orders 40,000 )
I also have Peel and Seal glassines in 4 sizes - also made in the UK by the same manufacturer.
The Lindner Glassines are made in Germany