The difference between parfum and eau de parfum is a slightly lower perfume concentration. The 100 ml packaging is small enough for you to bring in your carry-on on a plane.
From The Perfume Shop
Yves Saint Laurent Libre Eau de Parfum Refill - 100ML
Parfumdreams
Yves Saint Laurent Women's fragrances Libre Eau de Parfum Spray Refill
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