Overhead Projector (OHP) transparencies used as mathematics teaching aids require specific material, thickness, and design standards to ensure durability, crisp projection, and clear visibility in brightly lit classrooms. 

The following technical specifications outline the ideal parameters for high-quality math OHP sheets: 

1. Material & Physical Specifications

• Base Material: Optically clear, premium Polyester (PET) film. It provides superior dimensional stability, tear-resistance, and lay-flat properties compared to older cellulose acetate.
• Sheet Dimensions: Standard A4 size (210 x 297 mm) or Letter size (8.5 x 11 inches).
• Thickness: 100 to 175 Microns (4 to 7 mil). Thinner sheets (under 100 microns) are prone to curling from the heat of the OHP lamp, while thicker sheets (150+ microns) offer excellent durability for repeated, year-after-year classroom use.
• Finish: Ultra-clear with a micro-porous or chemical coating that prevents the sheets from sticking together in storage and ensures excellent ink adhesion without smudging