The phrase "a closed envelope" is correct and usable in written English.
You can use it when describing an envelope that is sealed and not open.
Example: "Please place the letter inside a closed envelope before mailing it."
Alternatives: "a sealed envelope" or "an unopened envelope".
"They handed me a closed envelope with the number in it, but I never opened it.
If you use the back of a closed envelope, as Dickinson did in "A 496/497," you get three squat triangles, like faces of a flattened jewel.
All the forms were placed in a closed envelope.
Immediately at the end of the treatment, patients completed the ODI-I, NRS and GPE questionnaires, which were placed in a closed envelope, and physical therapists recorded the results of the bridge tests.
Besides, their anonymity was always preserved (in agreement with the Spanish Law for Personal Data Protection) by letting them randomly choose a closed envelope containing a username which would identify them in the system and a password.
We divided the patients into two groups by simple randomization using a closed envelope.
The decision of the study physician was stored in a coded closed envelope in order to blind the result from the results of the radiograph.
The cylinder and all of the tracheas were suspended vertically and were sequentially intubated by one of the investigators, so that the cuff centre was 4 cm below the upper tracheal edge, in a random order (closed envelope technique).
She took a prenumbered envelope from a box, opened the closed envelope, and informed about what type of individual intervention the participant should be given.
Allocation was obtained by telephoning an independent co-ordinator (closed envelope system).
In the second part, a coupled thermal and airflow simulation model is used to investigate whether the more closed envelope generates a summer overheating problem.
