I am a CPA and I use these for the client's tax returns and original documents. They are thicker that the other office supply stores and I re-order them every year. Very satisfied.
I have been using envelopes like these to archive documents for 30 years. I don't seal the flap I simply tuck it in so it is easy to access the documents. They are made of heavy bright white paper that holds up well for years. I like the fact that they are made in the USA. I will be a repeat customer.
Finally someone got it right!. The large business envelope opens like a small letter or card envelope. The opening is on the widest side for easy insert of multiple documents. No more trying to make them fit in long ways!