Friends, sisters & magic pants: is it so many years as friends or a single experience that bonds girls together forever? From the new movie The Sisterhood of the Traveling Pants, four actresses talk about becoming great pals while playing the tightest of best friends in the comfiest of jeans.

A summer without your friends? Hideous on so many levels. Especially since all girls come back from summer a bit older and a little ... changed. The golden rule: Do what it takes to keep the "forever" in Best Friends For ever. But can a pair of used pants do the job?

In The Sisterhood of the Traveling Pants, the Pants are3 symbolic of love and loyalty, the two ingredients author Ann Brashares feels are the basics of true friendship. Brashares stuffed all the love in the girls' hearts into one pair of jeans. But friendships are fragile. Things like boys, competition and time apart can get in the way.

Each of the four girls of Sisterhood, even the friend with the booty bigger than everyone else's and the jock with legs no jeans ever fit, looks hot in the Pants. It's something the girls hardly ever feel about themselves. And that is another way the Pants are magic. When you feel your best, you feel brave. When you're brave, you can rule the world.

Actresses Alexis Bledel, America Ferrera, Blake Lively and Amber Tamblyn didn't know each other before arriving on set. They tried on the Pants. They talked. Then, they went shopping. They had lunches and dinners together, and they laughed all the time. Their connection was real. And it grew. They shared stories and opinions about everything from social issues to guys.

It wasn't movie magic that bonded the buds. "People ask who's the funniest?" says Blake, the youngest at 17 and brand new to acting. "We talked about it together, and we were like, who is the funniest? We realized we've sort of become the same person. I don't know what it is, but something inside us is the same." Friends become friends for lots of reasons, but friends become lifers when they see themselves in each other. See which girl you relate to: Carmen, Lena, Tibby or Bridget. Or ... America, Alexis, Amber or Blake--the actresses who play those four characters.

And whatever you do, don't forget Rule #10: Pants = love. Love your pals. Love yourself.

AMBER TAMBLYN is TIBBY

Hardest Rule For "Tibs" To Follow

#10 Remember: Pants = love. Love your pals. Love yourself.

WHO is TiBBY?

Heads, your life is great; tails, it sucks. Tibby got tails.

Tibby tries not to be negative about life, but for what? Her parents have never been there for her, and the rest of the dumb world sees her how they want to see her--as a self-centered, cynical teenager. So fine, she'll go there. Because, unlike her friends--the only people who know the real Tibby--she has nowhere else to go for the summer.

Tibby is so certain pathetic losers are tittered everywhere that she makes a film, her suckumentary, to prove just how lame all people are--all people except her friends. But, if you ask her, even they can get way too into the whole "love yourself and love each other" psychology of the Pants. She loves them, but sweet isn't her thing. She's a realist, and she's stuck at home working a lame job all summer, OK?

TIBBY OR AMBER?

Cast as rebellious Tibby is actress Amber Tamblyn, who actually has a rather charmed life. Coming from a loving and creative home, you know Amber as Joan in Joan of Arcadia, a role that makes Amber a near veteran at interpretation of lessons learned the hard way, spiritual rebirths (big or small) and the often mysterious ways love is revealed.

Amber liked Tibby right away. "She marches to her own drum, and I was attracted to how she questions everything," says Amber, who sees things far more positively than Tibby. "Our similarities are few and far between." Tibby needs a hefty attitude adjustment, and gets one, tenderly, in the film's most dramatic unfolding. Who better to wear her soul on a sleeve than the actress who regularly talks to God?

"Tibby isn't going anywhere, metaphorically," says Amber, who has a thorough way of understanding each character. "I read the script and thought it's great for her to be the one who has to stay home and find out what she has there before she goes looking for anymore or anything else."

GIRL FRIENDS OR SISTER FRIENDS?

Helping Tibby is Bailey, played by actress Jenna Boyd. To foster an authentic on-screen relationship, Amber and Jenna hung out with a camera, doing what Tibby and Bailey do. "Jenna and I really went out and interviewed people, and we tried to find people who could be classified as losers," Amber says. "We talked to a guy who takes care of an island and shoots rats for a living! What we found is what Tibby finds, which is that people lead amazing and complex lives."

Amber admits she didn't read the book before she made the movie for actor reasons. Still, she definitely gets that the Pants are a symbol for love. And love, it seems, is something she has in buckets for her co-stars.

"We're just like, 'Blah, blah, blah, blah!'" Amber laughs. "We had more inside jokes than any friend I've ever had. I felt sorry for the director because he couldn't even get our attention sometimes. They're good girls. They're awesome."

AMERICA FERRERA is CARMEN

Hardest Rule for "Carma" To Follow:

#3 You must never say the "phat" while wearing the Pants. You must also never think "I am fat" while wearing the Pants.

WHO IS CARMEN?

It's the smart little voice in your head. But it's not in your head. It's Carmen.

Carmen is the Sisterhood's conscience. In the book, she finds the pants in a thrift store and almost throws them out. In the movie, it's a bit different, but it is nonetheless Carmen who says what needs to be said. Even when words are hard or scary or have never been spoken no matter how much they need to be, it's Carmen who can wrench the real feelings out of her friends. But she's not so great at digging into her own problems, with herself and with her hardly-there dad.

If the other girls each have an angel and a devil duking it out on their shoulders, Carmen has a big chip on each of hers. With divorced parents and a mother who's Puerto Rican, making her a half-white/half-Latin misfit in her eyes, Carmen needs to learn to accept herself as she learns to accept her father along with his new uber-suburban, so not Puerto Rican wife and stepkids.

She's a fish out of water in many ways, so even though she has courage, it's hard for her to breathe. "Wear them. They'll make you brave," Carmen tells the girls. This is how they'll face their summer apart. She is amazing at telling the truth.

CARMEN OR AMERICA?

The truth is, Carmen and actress America Ferrera, who is Honduran, both struggle with self-acceptance. America made a stunning debut in HBO's Real Women Have Curves, which tackled the issue of self-rebuke in the United States, where we idealize the likes of Jessica Simpson even though the majority of the population is non-white and not even close to camera-ready skinny. Carmen learns what America already knows. "When there's a physical thing about you that you can't change, it can be very frustrating because you don't know how to fit in," America says wisely. "The danger in that is you can learn to hate yourself and blame yourself."

America and Carmen also share the same beliefs about love and loyalty: "I have four sisters, and you can fight and get mad, but fighting never breaks the bond of what a true sister is. Like the Sisterhood, I trust that they'll still be there for me even when they are so mad they can't stand me!"

GIRL FRIENDS OR SISTER FRIENDS?

America has a message for girls. She wants you to try the thing that scares you most. "I missed out on a lot of experiences because I was afraid of making mistakes," she says. "What if Alexis or Amber had never tried acting?" Does she consider herself in the same league as Amber and Alexis? "I don't think like that!" she says. "But it's weird when I see Gilmore Girls or Joan of Arcadia because it doesn't seem real that they're my friends now."

Offscreen, America says she felt like a big sister to Blake, an academic peer with Amber and a Spanish insider with Alexis. "When we wanted to bug Amber, Alexis and I spoke Spanish." And Blake? "I didn't know how I'd feel about her because she's so popular and, you know, she likes Britney."

As the most avid fan of the books, America applied her newly learned Pants philosophies and immediately warmed to Blake. "I've always been the outcast, so it was great to fall in love with the kind of girl I admired in high school yet also resented. Blake's great."

BLAKE LIVELY is BRIDGET

Hardest Rule For "Bee" To Follow: #4 You must never let a boy take off the Pants (although you may take them off yourself in his presence).

WHO IS BRIDGET?

Bridget's motto: See a ball, score a goal See a boy, score a date.

On the surface, Bridget is fearless. She does two things better than her friends: soccer and flirting. As the girl with the magic touch on the soccer field, and the girl boys want to touch off the soccer field, she's got the "it" that makes others wonder how she does it so ... effortlessly.

But underneath the smooth moves, Bridget has a deep-down sadness stuffed. When she was 11, her mother committed suicide, and she hasn't faced her loss or the uneasy side effects with her dad. Another secret? She's the only girl who loses her virginity. Bridget is looking for love, like we all are, but Bridget thinks she'll get it by breaking Pants Rule #4. Poor Bee.

So think what you want about bold, beautiful Bridget. Because her friends are the ones who know you don't have to look too closely at the fearless power to see the blow of losing Mom physically and losing Dad emotionally.

BRIDGET OR BLAKE?

Bridget faces her worst fear by the time the Pants are back on her butt. The role required innocence, but someone who could also rip the skin off a soccer ball. Those are big cleats to fill. Newcomer Blake Lively was cast, and--wow!

Blake is impressive because she shares all of Bridget's best qualities and none of her negatives. "Bridget is completely dedicated and passionate," Blake tells us after coming home from school, where she is involved in more than a half dozen extra-curriculars. "Bridget's also completely fun and psychotic and can't keep still. I'm insane around my friends!"

But Blake upstages Bridget on the heavy stuff: "Her family situation is completely the opposite of my family. We are very close and, if there's a problem, we talk about it. And she thinks she's going to find what she's looking for in the guy. I don't give in to anyone or anything. I stay true to myself."

Blake is like a more blessed version of Bridget. Feel jealous? "Oh, please, don't say that about me! I would love to be the best at things, but I don't feel like I can do anything that turns to magic the way Bridget does with soccer or boys. I'm in musical theater at school, and I love it, but I can't sing or dance at all. I hope acting ends up being what I'm best at."

GIRL FRIENDS OR SISTER FRIENDS?

The other girls, while experienced at being on camera, didn't treat Blake like a total rookie. "They were wonderful to me," Blake says earnestly.

Who did she connect with the most? "I could never pick one over the others!" she says. "It was a blast, and we still hang out. The girls came to my school performance, and I was so flattered because they're busy celebrities but they showed up. That's so sweet."

Blake has a lot to learn from the girls: "I don't know what it is, but something inside us is the same. We all crack jokes, we all take care of each other, we're all loving. We had such a bond. They had to make us stop at times because we wouldn't stop talking and laughing."

ALEXIS BLEDEL IS LENA

Hardest Rule For "Lenny" to Follow: #1 You must never wash the Pants.

WHO IS LENA?

Lena is a swan that feels like a duck. Lena is smart, compassionate, considerate, and she has what so many girls want, which is to be easy on boy-eyes. Lena is also drowning in a deep puddle of self-doubt. Coincidentally, a near-drowning experience during her summer trip in Greece is when Lena's journey to true self-love begins.

Author Brashares says she based Lena's character on Artemis, Greek goddess of war. Unfortunately for Lena, the war is with herself. She isn't pleased with herself. Double that for her boy skills, which she isn't sure exist.

Thank goodness for her friends. And for the magic Pants, which Lena sort of "washes" when she's saved from drowning by someone who finally sees more than just her beauty. So while her character is based on the proud, boy-hating Artemis, it's not until Lena believes in her own power and self-worth that she resembles the goddess.

Girl empowerment aside, sometimes a sister needs a boy to tell her she's awesome before she believes it. Could those friends of hers have been right all along?

LENA OR ALEXIS?

Lena's beauty is the source of her vulnerability, a quality that could accurately describe actress Alexis Bledel. Alexis started as a teen model. She remembers how stylists, agents and photographers zeroed in on her "flaws," giving her a self-consciousness in those early days not all that different from Lena's.

Lena has to grow up, something Alexis gracefully managed on national TV. "At the beginning, you see Lena as uncomfortable with herself physically," says Alexis. "At the end, she's much more confident. She learns to open up."

Alexis and Lena are also both artists (Lena paints; Alexis acts), and they have exotic bloodlines. Lena is Greek. Alexis is half-Argentinian and speaks terrific Spanish. She unleashed her rolling R's the first time she talked to Spanish-speaking co-star America on the phone, and America was like, "You? The Gilmore girl speaks Spanish?"

GIRL FRIENDS OR SISTER FRIENDS?

If pretty is the problem, then what's the question? Alexis's eves are a striking shade of blue, and she's reserved and not interested in hogging attention. Quiet girls often get judged as standoff-ish. The girls knew that wasn't true of her, and dug Alexis for who she is.

The other actresses might be rowdier, but Alexis was right there with them for the inside jokes and daily hanging out--and still is. "I've never worked with people my own age, and we all get along really well," Alexis says. "Amber said it perfectly because she said that if even one of us didn't have a sense of humor, then this whole thing wouldn't work."

The girls are tight enough that none of them would share in detail about their infamous humor, but they all suggested they are big dorks together on and oft camera. "We're more spastic off" camera than we are on, which is already kind of ridiculous," she says. "They [the Sisterhood] know each other so well, so to fake that would have been really hard. It's just luck that we liked each other so much. It's been really fun."

Sisterhood Rule #1

You must never wash the Pants.

Sisterhood Rule #2

You must never double -cuff the Pants. It's tacky. There will never be a time when this will not be tacky.

Sisterhood Rule #3

You must never say the woird "phat" while wearing the Pants. You must also never think "I am fat" while wearing the Pants.

Sisterhood Rule #4

You must never let a boy take off the Pants (although you may take them off yourself in his presence).

Sisterhood Rule #5

You must not pick your nose while wearing the Pants. You may, however, scratch casually at your nostril while really kind of picking.

Sisterhood Rule #6

Upon our reunion, you must follow the proper procedures for documenting your time in the Pants.

Sisterhood Rule # 7

You must write to your Sisters throughout the summer, no matter how much fun you are having without them.

Sisterhood Rule #8

You must pass the Pants along to your Sisters according to the specifications set down by the Sisterhood. Failure to comply will result in a severe spanking upon our reunion.

Sisterhood Rule #9

You must not wear the Pants with a tucked-in shirt and belt. See rule #2.

Sisterhood Rule #10

Remember: Pants = love. Love your pals. Love yourself.

Be a slacker

You've heard the saying: "He'd give the shirt off his back:" Well, a crew of celeb sisters are going one better--they're donating their pants for charity. Along with the Sisterhood stars, a slew of female celebs are each decorating a pair of Levi's to be auctioned for Girls Inc. Raven Simone, Britanny Snow and Kirsten Storms (just to name a few) will lend their artistic skills to the piles of paints. Wanna snag a pair? The auction runs May 23 through June 2 on ebay.com.