PURPOSE: To improve the straight advance properties in drill processing by specifying the diameter of the glass fiber monofilament of a glass fabric and the thickness of the glass fabric.

CONSTITUTION: The diameter of the glass fiber monofilament of a glass fabric is set to 3 - 8μm and the thickness of the glass fabric is set to 30 - 120μm. the main element component of the glass fabric is hard silica and becomes the resistance of drill processing and a surface is not smooth because of the fabric to generate undulation. Therefore, by making the diameter of the glass fiber monofilament fine and making the glass fabric thin, the undulation of the fabric is reduced to develop effect in straight advance properties.