Made of fine wood.
These EMERY BOARDS, inflexible wood, are particularly recommended for "fragile" nails. They have 2 emery particle sizes: the yellow, rougher side of the emery board is for an eventual preliminary filing and may be used for men' nails(generally thicker and harder) and for toenails; the thinner, lighter colored side allows precise filing.
How to use:
Use the lighter colored side with long and supple movements, stroking from the edges to the center to give your nails the shape you wish. To keep nails strong, avoid filing deep into the sides of the nail tip. To finish the work, eliminate any asperity by filing with small vertical strokes, from the top to the bottom and vice versa (bevelling), with the tip of the board. It also allows the nail layers to be sealed again.