Which synthetic fiber is widely used in the manufacture of modern bulletproof vests for personal body armour?

Introduction / Context:
Modern personal protection equipment used by police and armed forces relies heavily on advanced materials. Bulletproof vests and helmets are made from special fibers that can stop high speed projectiles. This general knowledge question checks whether you know the name of the famous synthetic fiber that is standard in many bullet resistant vests and other protective gear.

Given Data / Assumptions:

• We are talking about bulletproof vests and body armour, not ordinary clothing.
• Four fiber or material names are given: Nylon 66, Terylene, Kevlar, and Lexan.
• The question asks which fiber is used widely for bulletproof vests.
• We assume normal modern ballistic armour technology.

Concept / Approach:
The key is to recall which brand name has become almost synonymous with bullet resistant fabric. Kevlar is a synthetic para aramid fiber developed by DuPont. It has very high tensile strength to weight ratio, excellent resistance to impact, and good heat resistance. Because of these properties, layers of Kevlar fabric can absorb and disperse the energy of bullets and shrapnel. Other fibers like Nylon 66 and Terylene are useful for textiles but are not the main choice for ballistic vests.

Step-by-Step Solution:
Step 1: Recall common materials used in bulletproof vests from science and current affairs, such as Kevlar and high density polyethylene. Step 2: Identify Kevlar in the option list as a well known para aramid fiber used in ballistic armour. Step 3: Recognise that Nylon 66 and Terylene are general purpose synthetic fibers used mainly in normal clothing, ropes, and industrial applications. Step 4: Note that Lexan is a brand name for a polycarbonate plastic often used for transparent shields, not for woven bulletproof vests. Step 5: Conclude that Kevlar is the correct answer.

Verification / Alternative check:
If you consult basic science encyclopedias, defence technology articles, or even newspaper reports on body armour, you will repeatedly see references to Kevlar vests and Kevlar helmets. Some modern vests may use newer fibers or ceramic plates, but the traditional exam fact and widely accepted answer remains Kevlar as the main bullet resistant fiber layer. Cross checking with standard GK books confirms this.

Why Other Options Are Wrong:
Nylon 66: Strong and durable, but not primarily used as the main ballistic fiber in bulletproof vests. It lacks the same high performance ratio as Kevlar.
Terylene: A polyester fiber used for textiles, garments, and some industrial uses, but not the standard for making bullet resistant vests.
Lexan: A tough polycarbonate plastic used in safety glass, riot shields, and helmets, but it is not a fiber woven into bulletproof jackets like Kevlar fabric.

Common Pitfalls:
Students sometimes assume that any strong synthetic fiber, such as Nylon, must be used in bulletproof vests. Others may confuse Lexan because it is used in protective equipment but mainly in rigid transparent shields. The safest strategy is to memorise that Kevlar is the classic exam answer for bulletproof vests and to associate its name strongly with ballistic protection.

Final Answer:
The synthetic fiber commonly used in making bulletproof vests is Kevlar.