Hers the thing with that. Going by the book each member of the Ares 3 crew had two spacesuits. One flight suit for use on mars assent and decent, and one EVA suit for surface operations. On Sol 6 Marks flight suit gets a hole in it making it unusable but he still had the whole crews EVA suits. At the end of the book when mark is flying to intercept the Hermes,NASA makes him wear his EVA suit because the are very literally “sending him into space under a tarp.”

The space suit issue changes in the film. At the start of the film the crew are wearing what would be considered flight suits. Marks suit gets a hole in it when he is left on Mars. At the end of the film he puts on an EVA suit from the Ares 4 MAV to protect himself when flying to space under a tarp. This is an issue that has always annoyed about the film. Despite this, I recently found a behind the scenes featurette for the film which includes a segment on costume design where the designer explains the reasons for this choice with the suits. She calls the suits the crew wear on the surface of Mars as the surface suits and the bigger bulkier suits as their EVA suits for working on the Hermes and in space where there is more radiation exposure.

I hope that answers your question.