I think I have proven Marla is not real, along with many other characters (including Bob). I made a whole site for it and will try to summarize some key points here, but I strongly advise you to visit the site for more details.
Marla and Tyler Dress the Same
One of the first clues that Marla is not real is her likeness to Tyler. [...] Tyler’s hair is styled and worn almost identical to Marla’s throughout most of the film. Marla and Tyler are both seen wearing a similar faux fur coat, wearing sunglasses, almost identical rings and they are seen smoking in virtually every scene in the film. Even the framing of the shots is nearly identical when they are shown wearing similar clothes as well as the same facial expressions.
Marla and Jack (Edward Norton) Dress the Same
This is even more telling than Marla’s likeness to Tyler, but slightly more symbolic. Jack (the narrator, Edward Norton) is seen gradually looking more like Marla up until the final scene where we see the silhouettes of the two standing together, holding hands. From the back, it is virtually impossible to tell who is who. Note how Jack’s long coat and lack of pants have made it seem as if he is wearing a dress, a near perfect mirror image of Marla as they watch the 12 skyscrapers be demolished.
Marla Has No Reflection, Neither Does Tyler
Marla and Tyler do not have reflections, because they do not exist. Unless Jack is with Marla (or Tyler) their reflection or image will not appear. This is because this is the only time Marla is “real” to the narrator. We can see a great example of this in the scene when Tyler is saving Marla from suicide and goes to her hotel to save her. [...] When they both walk by, neither of them has a reflection. [...] The reason we see that Tyler and Marla have reflections in other scenes [...] is because at those points Jack was acting his himself observing the alter personality as a separate person. In the scene where Tyler goes to save Marla, Jack is supposedly not there, meaning Tyler and Marla are not actually being observed (except by us). We are being told to “imagine” what it would be like to see Tyler and Marla escape the hotel and in doing so the illusion of Marla and Tyler’s existence begins to disintegrate. We are not watching Tyler save Marla in this scene, we are watching Jack leave the hotel completely alone, yelling at the paramedics franticly about how Marla is infectious human waste (hence the user of the 3rd person when Marla is yelling at the paramedics.
Jack Becomes Marla In the Laundromat
In the laundromat scene we watch Marla take control over Jack, becoming his primary alternate personality. Marla opens 2 Speed Queen brand dryers and takes out multiple pairs of men’s blue jeans. She then walks to the vintage clothing store and sells them. [...] If Jack is Marla then this means he is selling his own pants to the thrift store and figuratively surrendering his masculinity. [...] Is there any other article of clothing that is more representative of Western “masculinity”? It is obviously a deliberate metaphor for Jack’s masculinity being hijacked by Marla, his alter-ego.
Later in the film we see Marla wearing a pink bride’s maid dress she claims she “got at a thrift store.” What if Jack, acting as Marla, bought this dress at the same time he sold his own jeans? This would make perfect sense since Marla is seen selling her clothes at a vintage consignment store, which is for all intents and purposes the same exact thing as a thrift store. Marla is likely hinting at this when she says to Jack, “you can borrow it sometime,” since she knows it is actually Jack’s.
At the end of the film we watch Jack run around frantically, without pants, after he has decided he wants Marla instead of Tyler and Project Mayhem. He has abandoned his masculinity entirely and is either accepting his emasculated self or is literally becoming a woman, depending on how you interpret the film. This culminates in the final scene where we see the mirror image of Marla and Jack holding hands. Jack creates Bob, then Marla, then Tyler, then finally betrays Bob and Tyler to accept his place as Marla (notice how Bob and Tyler both die the exact same way: a gun shot wound blowing out the back of their heads).
Marla Becomes Tyler On the Airplane
The first time we meet Tyler in the film is on the airplane. [...] On the plane Jack is talking to a middle aged black woman who is wearing sunglasses that resemble Tyler’s (see below comparison) and sitting next to Jack eating a meal. Jack then begins fantasizing about the plane breaking apart mid-flight after it collides with another plane. After he snaps out of this fantasy, Tyler is now sitting in place of the woman. How on Earth could this be possible..? (“It’s called a changeover. The movie goes on, and nobody in the audience has any idea.” - Jack)
This means the woman does not exist and Jack is likely sitting alone, either talking to himself or imagining himself talking to the woman and to Tyler. We watched a woman turn into Tyler, sitting right next to Jack. [...] Furthermore, we see the woman is somewhat older and eating from a tray, which is an interesting parallel to how Marla provides food for herself: stealing Meals on Wheels trays of food. This scene denotes the transition from Marla being the prominent alternate personality of Jack, to Tyler taking over.
Jack boarded the plane as Marla, the destruction sequence is showing us the “end” of Marla and then he “becomes” Tyler. This explains why he loses his baggage once he gets off the plane and is so confused as to why it was vibrating. Jack didn’t pack his bag, Marla did! He is now Tyler, and this is why the damaged cardboard box is the only luggage left on the conveyor belt, since this is Tyler’s luggage.
Fincher could not have made this much clearer when you consider the emergency exit sign above the door [...] You can tell the female turns into a man by the change of clothing and hair between the first and final image of the emergency exit diagram.
Testicles and Balls, Marla is Jack Post-Testicular Cancer
One of the weirdest aspects of Fight Club is the fixation on testicles. If you look at the film as a commentary on the emasculation of men in Western culture, it makes sense. But it goes deeper and helps explain why Marla and other characters are not real. There is an over-arching theme of “removing” manhood throughout the film. Whether literally removing someone’s testicles or through references to sex toys. In either case it suggests the removal of what defines a man.
If Jack is Marla then it makes sense that Bob and Marla are both members of the testicular cancer group. Jack feels emasculated, at first he only feels moderately insecure, so he imagines Bob there to help cope with his insecurity and anxiety about his actual testicular cancer. He then creates Marla, who helps him cope but also represents his feeling of being literally feminized by the prospect of losing his balls. If most of these things are not happening at all or are happening differently than they are presented (i.e. interactions with Marla, the support groups, etc.) then this evidence lends itself to the theory that we are simply seeing Jack’s insecurities leak into the narrative through the coping mechanisms he created to suppress them.
Dildos, Dildos Everywhere
Dildos are extremely prominent throughout the film and lend a lot of credibility to the fact that Marla is not real. Dildos represent the fact that Marla is taking Jack’s masculinity or that he is surrendering it, and this could likely be a metaphorical device used to illustrate Jack literally no longer physically has his testicles.
Another significant place we see a dildo is on Marla’s dresser, which is a very interesting place for it. When Tyler goes to save Marla, he leans against the dresser, causing the dildo to move. Marla then says, “Oh don’t worry, it’s not a threat to you.” This could be interpreted a number of ways. If Marla is Jack, and Jack is Tyler, then the dildo is likely not going to be used by any of them, so it is literally not a threat. In addition, if Tyler is a coping mechanism who represents masculinity, he presumably actually has a penis – so the dildo is not a threat – while Jack who has been possibly physically emasculated would see the dildo as a threat.
In addition, the positioning of the dildo on the dresser and next to the door lends itself to another interpretation that I feel makes more sense. If Jack believes that this is where Marla stays, yet he is Marla, then this is a clever way of communicating to the viewer that Jack is leaving his manhood at the door when he arrives and takes on the role of Marla. This would also help add even more strength to my vibrating suitcase theory (below).
The Vibrating Suitcase (Dildos Part II)
This is one of the strongest points for Marla’s non-existence. The most interesting part about this scene is that Jack is utterly confused. If he had been the person to actually pack his bags, then surely he would understand what COULD be vibrating in the suitcase. The security guard even says, “9 times out of 10 it’s an electric razor.” But Jack continues to look at the security guard confused and says, “my suitcase was vibrating?” Implying he has no idea what could possibly be the cause.
However, if Jack is actually Marla, then Marla is likely the one who packed his bags. Which means there actually is a dildo in the luggage. Jack acts totally confused about this because he himself has no idea he is Marla. [...] The security guard even hints at this by saying, “of course it’s company policy never to imply ownership in the event of a dildo, we have to use the indefinite article a dildo, never your dildo” and looks at Jack skeptically. [...] This is brilliant because the security guard is essentially saying we cannot say it’s actually Jack’s dildo, because we do not know he is Marla, it is indefinite and ambiguous on purpose.
Marla and Jack Live In a Hotel, the Paper Street House Doesn’t Exist
The house Tyler lives in, where Jack moves into and Project Mayhem uses as a base does not exist. Equally interesting is Marla does not have an apartment…or a house…she lives in a hotel. [...] Who else do we know that spends almost all of his time in hotels? Oh right, Jack. When Marla calls Jack to tell him she is committing suicide, Jack says, “just picturing Marla throw herself around her crummy apartment” but we know that Marla is staying at a hotel because the exterior shots of her “apartment” have a neon sign in the background that says “Rooms”.
In the beginning after meeting with Tyler after his condo explodes, Jack says “ah, I need to find a hotel.” After Jack’s condo exploded, he met with Tyler, said he needed a hotel, and actually went and got one. He did not go to the Paper Street house, because it does not exist. This explains why when he handed the beer to Tyler, the neon sign in the background went out (which is a visual representation of his masculinity…it’s an actual penis). He was transitioning back into Marla and turning off his masculine persona. Tyler and Marla’s residences are the exact “same” residence, in that it is only the hotel Jack is living at but he is imagining two separate places for his two separate alternate personalities. He has multiple people living in one “house” which also serves as a clever metaphor for his psyche.
This helps explain Jack’s distaste when Marla begins spending more time at the Paper Street house, why Tyler and Marla cannot be in the same “room” together (because he cannot be two people simultanousely) and why Project Mayhem causes the Paper Street house to turn into a “living, breathing thing”. Jack says, “She invaded my support groups now she invaded my home” and explains why Tyler is adamant about not being in the same room. The personalities are losing their compartmentalization (think about it, Marla begins living at the Paper Street house even, then Bob moves in and Project Mayhem, they all wind up in one house or one “compartment”) and Jack is losing his sanity as a result, which we watch deteriorate through the rest of the film.
Tyler Saves Marla from Committing Suicide
Even Jack says “now why would Tyler think it’s a good idea to save Marla?” This is partly a sly reference to the twist ending, where we discover Tyler is Jack. But if you take this deeper you realize it’s because if Marla dies, Jack dies, meaning Tyler also dies. If Marla is committing suicide and she is also Jack, then it means Jack will die as well as Tyler. In other words, we are watching Jack lying in the bed trying to commit suicide – “calling” Tyler at the non-existent Paper Street House. This is the incentive for Tyler to save her. If Jack dies, everyone dies.
Left In the Copier
Jack’s boss finds the fight club rules in the copier and confronts Jack about them. Jack replies with something Tyler might say, then says “Tyler’s words coming out of my mouth. And I used to be such a nice guy.” Immediately following the phone rings and it is Marla saying she thinks she has breast cancer. [...] Is it really a coincidence that Marla calls him right after we see Jack being taken over by Tyler’s personality (i.e. the words he chooses to use to tell his boss off?) This is Marla saying to him that she is basically dying and her personality isn’t needed anymore, she’s trying to get his attention so she can continue to exist to Jack. [...] Jack has just been found out along with his association with Fight Club, an enormously panic-inducing experience, triggering the need for his coping mechanism, Marla, to help him through the ordeal. Right on cue, the phone rings and it is Marla to help get him out of the situation, literally asking him to leave work immediately and come to her house to check her for breast cancer.
Self Improvement is Masturbation
This is a big one. There are a ton of references to masturbation and “fucking yourself” throughout the film. The most notable scene is where Tyler and Jack board the bus and Tyler says, “Self improvement is masturbation, now self destruction…” and trails off. [...] Fast forward to when Tyler saves Marla and they are now in the habit of constantly having sex with each other. If masturbation is self improvement, and if Marla, Tyler and Jack are all the same person, then Jack is masturbating. In the scenes where Tyler and Marla are having sex and yelling, what is Jack doing? He is engaging in self improvement. He is shown reading and exercising while the house is literally being destroyed and falling on his head.
Infectious Human Waste
Everyone remembers how Tyler Durden makes his soap – stolen fat from the liposuction clinic. In the scene where they go to steal the fat they alert the attention of the security guard (more on this later) and hide behind a dumpster marked “infectious waste”. To be more specific, the contents of the dumpsters are in fact infectious human waste. When Tyler had gone to save Marla, we see her yelling at the paramedics and emergency responders that are coming to save her that she’s “infectious human waste.” Even more interestingly she is speaking about herself in the 3rd person. This makes perfect sense since Marla is Tyler and in this scene we are actually watching Jack running away from the hotel and speaking about Marla. [...] What are the odds that Marla, if she were her own individual person and not a figment of Jack’s imagination, would choose to use the word’s “She’s infectious human waste!” to describe herself in the third person when we know that Jack and Tyler literally use infectious human waste to make soap. This is a deliberate connection the director was trying to make.
“I Want to Have Your Abortion”
After Tyler and Marla have sex Marla famously says “I haven’t been fucked like that since grade school.” This line in the film was actually improvised by Helena. The actual line in the script is “I want to have your abortion.” This is an odd choice of words even for someone who is supposed to play a dark and cynical character like Helena – it kind of doesn’t make sense. However if you consider that Marla is Tyler and Jack, then Jack is fucking himself, and will ultimately destroy himself – essentially an abortion of himself. This makes her choice of words make much more sense. “Self improvement is masturbation, now self destruction…” is related to this also. [...] Marla is Jack, Jack is also Tyler, when Marla and Tyler are done having sex she says “I want to have your abortion” which is the same as self destruction, since they are the same person.