"I hadn't played a character who was so the opposite of the sort of strong, strident, more obviously passionate women that I think I've played in the past," said Winslet, who has been nominated for six Oscars, winning the best actress trophy for her role in The Reader as a Nazi concentration camp guard trying to conceal her past in 1950s Germany.
"I was keen to explore somebody who was much more introverted and fragmented," she says. " . . . I was fascinated by that. I had played mothers, but I hadn't really played a single mother to a son of that age. And that's a particularly interesting dynamic. . . .
"Also, I was drawn to the unexpected nature of the love story, which I found very moving."
Labor Day, which premiered in September at the Toronto International Film Festival and landed Winslet a best actress Golden Globe nomination in December, opened in theaters Friday. Reitman, who made Up In the Air and Young Adult, is likewise trying something different here. The film's tone is lushly romantic one minute, edgy and suspenseful another, and then, unexpectedly, something will happen that is funny and odd.
"Actually, I didn't find the script, initially, humorous in any aspect at all," Winslet confessed on the phone from London. "I was actually quite surprised myself when I first saw the movie that there were a couple of moments when I found myself laughing in spite of the moment."
Winslet, 38, was "very, very pregnant" when interviewed in late November. A few weeks later she was in a different kind of labor: On Dec. 7, she and her husband, Ned Rocknroll (nephew of Virgin billionaire Richard Branson), became parents of a baby boy, Bear. The actress has an older daughter and son, from respective marriages with film crew veteran Jim Threapleton and director Sam Mendes.
Adele's transformation in Labor Day was tricky for Winslet. There was the danger of playing the indrawn, quaking, agoraphobic Adele with too much outward expression, and then the challenge of showing the sexually and spiritually reawakened woman without overplaying that, too.
"One can always be heavy-handed, and I'm not always the best gauge of how far I'm going, or how much further I maybe need to go," she said.
"One of the lovely things about acting is . . . putting another person together," Winslet added. "But putting a person together who's got so much missing from their spirit was an interesting new thing for me to do. . . . Her bones feel chalky, and her veins feel empty when you first meet her. And I just didn't want her to be that way all of the time.
"So I knew that I had to just bring some softness and some warmth and color into the character, as she gradually does come back to life, through falling in love. And through finding herself again.
"And, you know, this is a woman who did have a really big heart. And actually, even though it doesn't appear so at first, she was a good parent. To the best of her ability, she did as much as she could for that child, and he's a good boy, and that is in part largely to do with her and her consistency of love for him.
"She isn't sinking into a bottle of gin in the afternoon. She isn't hooked on prescription meds. She just about pulls it together, she just makes it OK for him to cope alongside her on a day-to-day level. . . .
"There was a big, pulsing, passionate woman in there once, and she simply has forgotten all of that after what she has gone through."
Next up for Winslet is The Dressmaker, an adaptation of Rosalie Ham's 2000 novel, to be directed by Jocelyn Moorhouse later this year. And the actress tries something different again in Divergent - playing an out-and-out villain to Shailene Woodley's teenage heroine - in the Hunger Games-ish sci-fier, which opens next month.
Asked to look back at her career, Winslet considers three projects especially important to her development as an actress.
One is Eternal Sunshine of the Spotless Mind, the 2004 Charlie Kaufman/ Michel Gondry love story/reality check in which Winslet plays a free spirit named Clementine, with the orange hair to match.
" Eternal Sunshine really opened me up a lot," she said. "I couldn't be in any way self-conscious playing that brash, loud character. And really, having to do a good American accent . . . I had to pull that off. I really felt like I had some personal breakthroughs within that experience that carried me into other things."
Winslet cites Little Children, Todd Field's 2009 take on the Tom Perotta novel, in which she played a mother and housewife who falls into an affair with a stay-at-home dad, as another formative experience. So, too, her Emmy-winning performance in the Todd Haynes-directed telefilm, Mildred Pierce.
"Actually, it's very much about confidence-growing," Winslet reflected. "Acting is so much about just actually having the confidence to step out there and do your best. And forget everything else . . . all the fear, all the pressures that you put on yourself, and actually learning how to get rid of that stuff. And that can take quite a long time."