Heidi Klum feels ''free'' when she's naked.

The 41-year-old supermodel admits she regularly lies in the sun topless because she hates tan lines, and she has always comfortable stripping off in public because her parents took her to nudist beaches was growing up.

In an interview in Us Weekly magazine, the German beauty said: ''People laugh when I say this, but I grew up going to nude beaches with my parents. It was very free. I took my top off, and I still do. I don't like to have tan lines on my boobs.''

Heidi is considered to be one of the world's most beautiful women, and works hard to stay looking great.

But the 'America's Got Talent' judge insists she isn't ''ageless'' and can notice a difference in her body and looks.

She said: ''If you put me a 20 year old next to me, of course you see a difference, but that's normal. I'm not trying to be like, 'I'm 20!' Because I'm not.''

Heidi - who has four children, Leni, nine, Henry, eight, Johan, seven, and Lou, four, who she jointly raises with her ex-husband Seal - is very strict with her diet and exercises regularly to maintain her trim figure, but has stopped weighing herself.

The catwalk queen - who is currently in a relationship with 27-year-old art dealer Vito Schnabel - said: ''I go up and down at times, which is tricky for my stylist. It's like, 'Oopsie!' But we just take the dress out. My scale ran out of batteries a year ago, and I never put new ones in.''