Bulletproof vests are available in different grades which depends on the material from which they are made.
As far as the legality regarding wearing bullet proof vests in public is concerned, police and armed forces are for sure permitted to wear bulletproof vests in almost all parts of the world. Although for civilians, it is a matter that depends upon the laws in their state or country.
In India, as per law of Government of India (Indian Arms Act 1959 & Indian Arms Rule 1962) there is no clause for sale & use of Bullet Proof Body armor & other Bullet Proof or Blast Proof Products in India. However, generally sellers of bulletproof vests in india make sure that the bullet proof vests are not sold to minors or persons with some criminal records.
In the US, persons who have been ever convicted for any crime are not legally permitted to wear bulletproof vests. Not only this, they are not even permitted to possess it.
In Canada, a person can legally own a bullet proof vest in almost all provinces of Canada. Although in provinces like Alberta, Manitoba and British columbia it is prohibited. However, in British Columbia a person must have a government-issued license to use it.
In Italy, as such there is no constraints in wearing bulletproof vests and other body armors, however, they are exclusively allowed for military personnel but legally forbidden to civilians. In Italy it is mandatory for private security officials to wear bulletproof vests while on duty.
In European countries, using and selling bullet proof vests is permitted in most places. However a serious restriction is imposed over something considered by the law as “armament materials”, which are not allowed to be used by civilians. Although many shops in Europe openly sell bulletproof vests, but most shops won’t sell to those who have past records of crime.
In conclusion, legality of possessing or wearing a bullet proof vest is dependent upon the factors like profession –a security personnel and criminal record of the person, if any, who is not a security personnel rather a civilian. Besides, one should also need to find out the other legal rulings for the particular state or country.