The recommended fill materials are based upon your application requirements - flexibility, stiffness, abrasion, chemical or corrosion resistance. 

Standard Bristle material

Brass
Rustproof and spark resistant, brass provides a gentle brushing action, which is softer than steel wire. Suitable for working with mild bleeches, mainly used for processing of nonferrous metals

Brass coated steel wire
Uses the qualities of standard carbon steel but with rust –proof coating. An increase brush life and adds higher tensile strength and cutting performance.

Carbon steel wire
Available in a variety of sizes, straight or crimped. This is a widely used metal fill material. It has excellent abrasive ability and high fatigue resistance for long brush life at a low cost. Typically used in applications where abrasion is required in dry environments, general cleaning, rust removal, deburring, edge blending and roughing for adhesion.

Cotton/ cotton Swab
Cotton swabs provide maximum absorbency and smoothness. Best used in non-abrasive cleaning and polishing applications

PVC
An economical material with reasonable flex life, low friction resistance and no loss of stiffness in water.

Polypropylene 
Resists abrasion and most acids and solvents. Does not absorb moisture, adores and sheds dirt easily. Typically used for applications in corrosive environments with acids and alkalis. Polypropylene is a versatile plastic that stays stiff when wet. Heat tolerant to 110° C.
Note: not UV stable.

Natural and Animal fibers
Generally used in washing, light deburring and polishing applications. Fibre consists of heat resistant plant fibre, is slightly abrasive and therefore can be used for smooth grinding, above all for working on wooden surfaces. Fibre is used for general cleaning and polishing work

Nylon 
Tough and long wearing, Nylon discourages bacterial growth and resists most acids. Excellent for industrial and food service applications. Nylon is the most widely used fill material for brushes. It is the longest lasting and most versatile brush fill material. Nylon far out wares any of the other fill materials in most applications. Nylon will absorb some moisture thus reducing stiffness.

Stainless steel wire
Generally used for wet and rust applications. Available in a variety of sizes, straight or crimped. Highly corrosion and heat resistant. Ideal for applications that involve stainless steel or aluminium. Will not leave ferrous deposits, however ferrous deposits will occur if the brush is used on ferrous applications prior to use on non-ferrous materials

Technical information
The main factors that affect brush wear are bend recovery, abrasion resistance, bristle size, brush speed and fatigue resistance. 

The stiffness can be recovered by increasing the diameter of the bristle. Relative stiffness of bristle in a brush is directly related to the diameter of the bristle and inversely related to the length of the bristle in the formula: relative stiffness = diameter squared over length cubed. (RS=D²/L³) 

Brush speed as expected affects brush life. Abrasion rate increases as speed increases. This is caused by the fact the more times the filament comes in contact with what is being brushes the more times it impacts and flexes the filament

Bend recovery is the ability of a bristle to flex and then return to its original position. Bend recovery of a brush fill material is partly an inherent property of that material.

Abrasion rate of a brush filling material is primarily an inherent property of that material. In the case of synthetic filaments, it is essentially a property of the material from which the filament is made.