The polypropylene wedge-shaped shim has a black color. Polypropylene (PP) is a strong, lightweight plastic with a hard, smooth surface that is suitable for use where bacterial buildup could be a factor. Typically stronger, more rigid, and more resistant to higher temperatures than polyethylene, polypropylene also has good resistance to chemicals and solvents.

Plastic refers to a group of synthetic or semi-synthetic materials that have been engineered to achieve specific properties. The most notable characteristics of plastics are its low weight, machinability, corrosion resistance, and typically good thermal and electrical insulating properties. Certain plastic grades also offer optical transparency similar to glass, low-friction or self-lubricating surfaces, and exceptional impact resistance. Depending on their properties, certain plastic grades can be used as alternatives to metal, glass, and ceramic. Unlike metal, plastic may experience creep, which is deformation caused by longtime exposure to a constant load.

Tensile strength, used to indicate the material's overall strength, is the peak stress it can withstand before it breaks. Corrosion resistance describes the material's ability to prevent deterioration caused by atmosphere, moisture, or other medium. Wear resistance indicates the ability to prevent surface damage caused by contact with other surfaces. Toughness describes the material's ability to absorb energy before breaking, while hardness (commonly measured as indentation hardness) describes its resistance to permanent surface deformation. Impact resistance is the measure of a material's ability to absorb a shock of energy before breaking.