September 04, 2013 at 06:02 PM EDT

The Pretty Little Liars summer finale just happened, but costume designer Mandi Line is already looking forward to the fan reaction to the show’s Halloween episode, which airs October 22nd. “The fashion is insane this season as far as fan appreciation goes,” Line told EW. “It’s not even that I’m taking more risks or doing anything that different. [The fans] have started to identify [with the characters’ style].”

In fact, audience appreciation for the sartorial elements of the ABC Family series is so overwhelming that clothes featured on the show have been selling out in stores. “Every time I go to [L.A.’s Una Mae’s in Los Feliz], they say, ‘We sold out of this necklace, or this dress,'” Line said. “These young girls save up their money and they can definitely afford [brands like] Free People. The bummer is… we’re shooting scenes now that won’t air until February, which makes it tough [to find things later]. Fans will say, ‘I wanted this one skirt and it sold out.’ The truth is it’s because I bought it 8 months ago.” Though Line is staying mum, a Liars-inspired clothing collection is rumored to be in the works, which would help solve the problem of supply and demand.

What will happen to the coveted costumes when production on season 4 ends in November? “Warner Brothers owns every single item and because our show is so big, that stuff goes into museums or it’ll go into archives,” explained Line. Even if a character has been killed off, their wardrobe remains under lock and key. “We inventory because, as everyone knows, just because [a character is dead], you’re never really dead on our show. We’ll retire outfits and put them away or give them to Warner Brothers to put into the archives, then all of a sudden, it’ll be like, ‘Nope. Detective Wilden. Flashback. Bring it back out.'”

And don’t be surprised if you see paparazzi photos of one of the stars in her character’s clothes during their downtime. “Troian [Bellisario] is going to London this hiatus and I get so excited when she asks [to borrow] things because she has such great personal style,” Line said. “The girls ask [to borrow pieces] all the time, but we make sure to have them sign [something] that says, ‘I took this, I took that.’ They’re good at getting it back to us. Except for, sometimes with Ashley Benson, we’ll have to actually [say], ‘Okay. Give me the keys to your car. Open your trunk and get it out!’ I love that girl, but she always goes, ‘Oh, no, it’s in my trunk!’ or ‘It’s at my house.'”

Click on to see Line’s favorite fashion moments from the Pretty Little Liars summer season, find out about the mystery behind the red coats, and get a sneak peek at the look of the PLL spinoff series Ravenswood

Emily’s “leggy” dress

Line’s favorite Emily outfit this season consisted of an All Saints dress, Michael Kors vest, and Frye boots. “I wore the exact outfit the weekend before,” she said of the look, featured in episode five. “I dress the girls how I either dress or want to do dress. [Shay Mitchell’s] got amazing legs, so she’s my aspirational me. [When I’m shopping], I go, ‘One for me, one for her.’ Emily never gets to wear dresses, so I thought, ‘Why doesn’t she wear a t-shirt as a dress?’ The leather vest keeps her edgy. The bummer about that outfit is that you never got to see it head to toe on-camera.”

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