‘Polar Bear’ sheds sympathetic light on fragile family

In 1978, when writer-director Maya Forbes was 10 years old, her mother went away to graduate school, leaving Forbes and her little sister in the care of their mentally ill dad. The girls, and even their mom, didn’t fully understand his diagnosis of bipolar disorder. Doctors still called it manic-depression in those days.

Dad was unable to work, so while mom pursued studies that would improve the family’s financial lot, he spent a year and a half raising their daughters in his own unconventional way.

Forbes draws on her childhood for her directorial debut, “Infinitely Polar Bear,” a quiet, personal film that plays as a cinematic love letter to her dad.

It may be overly ambitious, aiming to make race and gender secondary themes while depicting the toll mental illness can take on a family, but succeeds with compelling performances and a deeply heartfelt story about the father-daughter bond.

Cam Stuart (Mark Ruffalo) is crazy about his family, and also just a little crazy. He struggles with bipolar disorder, which his youngest daughter mistakenly calls “polar bear.” Wife Maggie (Zoe Saldana) still believes he’s a capable parent, even after a mental breakdown lands him in the hospital. She leaves him in charge of their young daughters, hoping the daily routine of making meals and taking them to school will provide healthy structure to his life.

The novelty wears off quickly for 10-year-old Amelia and 8-year-old Faith. They’re embarrassed by their dad – he can be overly outgoing and oblivious when others are uncomfortable – and ashamed of their apartment, where clothes, clutter and his half-finished projects cover every surface.

But there are upsides to Cam’s ways. He helps his daughters make friends when he spontaneously rallies the neighborhood kids into a basketball game, and he stays up all night making an elaborate, last-minute costume for Faith’s pageant. The girls begin to understand his fragility, and the caretaking becomes reciprocal.

Ruffalo appears in nearly every scene, and he’s excellent as chain-smoking Cam, infusing even his most erratic behaviors with a tender sweetness. Ruffalo makes Cam interesting to watch and easy to root for, even as he brings the mania and unpredictability of mental illness to life. Saldana gives Maggie a nuanced strength as a mother conflicted about how to provide the best life for her children.

Cam’s relationship with Amelia (a foil for Forbes) is the film’s emotional core, and Imogene Wolodarsky, Forbes’ real-life daughter, plays her with heartbreaking maturity. Clips of super-8 footage add to the film’s family feel. The credits reveal some were actually shot by Forbes’ father.

The story and performances are so sincere that “Polar Bear” doesn’t suffer much from its loose ends.

“Infinitely Polar Bear” is a deeply personal movie that paints a sympathetic portrait of a family affected by mental illness. It may be a rosy-lensed view, but anyone can understand such idealization of parental love. Forbes dedicates the movie to her mom and dad.