What is the Difference of PBT, PET, PP and Nylon for Brush Bristle Filament?

Firstly, what is the definition of each material:  

PBT Polybutylene terephthalate (PBT)[S1] 

Polybutylene terephthalate (PBT) is a thermoplastic engineering polymer that is used as an insulator in the electrical and electronics industries. It is a thermoplastic (semi-)crystalline polymer, and a type of polyester. PBT is resistant to solvents, shrinks very little during forming, is mechanically strong, heat-resistant up to 150 °C (or 200 °C with glass-fibre reinforcement) and can be treated with flame retardants to make it noncombustible. It was developed by Britain's Imperial Chemical Industries (ICI).^[2]For more details, please check: https://en.wikipedia.org/wiki/Polyethylene_terephthalate 

PET Polyethylene terephthalate

Polyethylene terephthalate (sometimes written poly(ethylene terephthalate)), commonly abbreviated PET, PETE, or the obsolete PETP or PET-P, is the most common thermoplastic polymer resin of the polyester family and is used in fibres for clothing, containers for liquids and foods, thermoforming for manufacturing, and in combination with glass fibre for engineering resins. It may also be referred to by the brand names Terylene in the UK,^[5] Lavsan in Russia and the former Soviet Union, and Dacron in the US. For more details, please check: https://en.wikipedia.org/wiki/Polyethylene_terephthalate

PP Polypropylene (PP)

Polypropylene (PP), also known as polypropene, is a thermoplastic polymer used in a wide variety of applications. It is produced via chain-growth polymerization from the monomer propylene. Polypropylene belongs to the group of polyolefins and is partially crystalline and non-polar. Its properties are similar to polyethylene, but it is slightly harder and more heat resistant. It is a white, mechanically rugged material and has a high chemical resistance.^[1] Polypropylene is the second-most widely produced commodity plastic (after polyethylene) and it is often used in packaging and labeling. In 2013, the global market for polypropylene was about 55 million tonnes.^[2]For more details, please check: https://en.wikipedia.org/wiki/Polybutylene_terephthalate 

Nylon

Nylon is a generic designation for a family of synthetic polymers, based on aliphatic or semi-aromatic polyamides. Nylon is a thermoplastic silky material^[1] that can be melt-processed into fibers, films, or shapes.^[2]:2 It is made of repeating units linked by amide links^[3] similar to the peptide bonds in proteins. Nylon polymers can be mixed with a wide variety of additives to achieve many different property variations. Nylon polymers have found significant commercial applications in fabric and fibers (apparel, flooring and rubber reinforcement), in shapes (molded parts for cars, electrical equipment, etc.), and in films (mostly for food packaging).^[4]For more details, please check: https://en.wikipedia.org/wiki/Nylon 

Secondly, in the paint brush Industry, most filaments is made from PBT and PET due to the following reasons:

1.PBT and PET can be tapered by chemical material;

2.PBT is soft, PET is hard, which combined together would be get the best effects for extruding the filaments;

3.The Characteristic of PBT and PET (High Temperature resistance and elasticity) is very suitable for making paint brush.

Most of brush filament is made for tapering because tapering would be making paint brush paint more smoothly. 

Thirdly, the following are the chart of characteristic of each material:

Lastly, what do we use these raw materials for?

1. PBT /PET:  Paint brush, Artist paint brush, broom brush, polish brush, bottom brush, toothbrush, horse brush, hair brush;

2. PET: cheaper broom brush, cleaning brush, horse brush;

3. PP: Clean brush, horse brush.