I needed an envelope that 10x12 papers would fit into. This was perfect even though bigger than I really needed. I just folded it over (contents fit width-wise) sealed it with tape and I had a double protected parcel.
I purchased these envelopes for mailing patient medical records. Quite a lot of documents fit in the envelopes and they have held up well. We had one returned for wrong address and the envelope and its contents were still in very good condition.