Nicky Hilton Rothschild's shoes have always been a ''really, really big deal'' to her.

The 35-year-old businesswoman had a strict school uniform as a teenager which meant the only way she could express her own style was through her footwear.

She said: ''I went to all girls, Catholic, private school on the Upper East Side. The only thing we could style ourselves was our shoes, so it was a really, really big deal...

''I have been wearing French Sole since I was in high school. We weren't allowed to wear any heels, so we had to choose a flat.''

And even now, the heiress - who has children Lily, three, and Theodora, 21 months, with husband James Rothschild - wears flats more often than heels because they are more practical.

She said: ''You definitely don't wear heels as much. Running around the city with a stroller, two children, a lot more flats.

''Which is great, because I love flats.''

Nicky is a particular fan of Christian Louboutin's famous red-soled shoes, and the designer created shoes for her wedding, the afterparty and a custom-dsigned pair for her wedding night.

She told Yahoo!: ''I love baby blue. I remember the first time seeing [Christian Louboutin's] shoes, I saw the red soles - and I thought that was so clever. I thought if I ever design shoes, I will have powder blue soles.''

Although Nicky is passionate about footwear, she admitted her sister Paris Hilton doesn't share her obsession.

She said: ''My sister, believe it or not, was always a tomboy, she didn't care about shoes. I care, I love the whole thrill of it.''