Subject 347 is an adult/young adult female, standing at 164cm tall, and 55kg in weight. Despite being a seemingly average woman between the age of 19 and 25, SCP-347 is completely invisible. This also includes everything inside her body at any given moment, although her waste products and saliva appear once they lose contact with her, but her blood, skin, and hair samples all remain invisible. Testing has confirmed that she has normal eyesight, despite the fact that the cones and rods of the eyes must be visible in order for a human to see. Subject 347 describes herself as being an average female of mixed race, with brown eyes and wavy black hair, and refers to herself as Claudia, although it is highly likely that this is a false name taken from the actor Claude Rains, the lead of The Invisible Man. Her true identity has not been ascertained.

Aside from her invisibility, Subject 347 has no unusual traits other than immense skill in picking locks, theft, and has been observed swallowing small objects in order to turn them invisible, displaying the ability to regurgitate them at will without dispensing all the contents of her stomach as well, a trick she claims she came up with after watching a Stevie Starr performance on a late-night show.

Subject 347 was recovered in Florida, after local news and rumors about a poltergeist inhabiting an abandoned house drew attention of facility staff in the area. After infrared cameras revealed that she still gave off a human heat signature, Subject 347 was quickly captured and after much deliberation willingly entered into Foundation custody, asking for warm food and protection from the elements. It has been theorized that she had been living on the street and in abandoned buildings for several years, although Subject 347 had adamantly refused to discuss such things. Two deaths and several apparent incidences of 'ghost activity' have also been attributed to her.

When first recovered, Subject 347 showed signs of mental instability and violent outbursts, as well as compulsive theft and bouts of refusing to speak for several days on end. Traditional counseling methods have helped reduce the frequency and severity of such issues, and it's theorized that with more time Subject 347 may heal from the trauma of years of not being seen and being completely alone.

It has been suggested that Subject 347 be introduced to other Subjects, as human contact appears to be quite pleasing, and she greatly enjoys being acknowledged without being seen as strange. When ignored, Subject 347 does not seem to demand attention, but rather toys with people by rearranging things and hiding things. When left alone with somebody who is sleeping or otherwise distracted, it should be noted that Subject 347 will touch and stroke a sleeping person, tuck in their blankets, and do other small things. Subject 347 has confirmed that this behavior just feels "right" although the person it's done to often describes it as "unnerving".

Although Subject 347 is invisible in all terms of visible light, she may still be observed via ultraviolet or infrared cameras.