Even for someone seeing body armor for the first time, there is an apparent difference in the look and feel of hard armor plates compared to soft ballistic pads. But, the real differences only come to light when you need to use the armor.
In the most basic of separations, soft armor is meant to protect from handguns and hard armor from rifles. And, it would be up to the user to determine if there is a need to go heavier or their activity would be better with only soft armor.
There are five characteristics that differentiate plates and ballistic threads:
The importance of each will depend on what you are planning to do. For the majority of domestic situations, even including law enforcement, soft armor will be enough to protect from an attacker. And, when you take into account that you must wear your armor for hours at a time, going lighter becomes the only option.
Also, the flexibility means that you can have more of your body protected, which is essential when it comes to danger from explosives.
But, when it comes to open combat, especially in urban environments, where you know you will be fighting against people with rifles, there is no option but the hard plate. It may only protect your torso vitals, but nothing else will stop a rifle round, and the protection will increase your survivability immensely.
Protective Characteristics
If we are to measure toughness alone, a good hard plate will always stop bigger and faster bullets than its soft counterpart. But, this durability comes with a price.
Namely, hard plates are roughly five times denser than a soft panel, making them relatively heavy. This is even the case for the lightest types of plates like UHMWPE. Because of this, a plate is usually used only to protect the torso and often leaves a lot of space on the side.
Wounds to these areas might not be instantly fatal, but they are still high-velocity gun wounds, and they do hurt like hell even with instant surgical action.
Soft armor will usually cover the body from all sides. Also, you can wear auxiliary soft armor that will cover other parts of the body, including the stomach and the groin. Finally, some options like the https://uarmprotection.com/product/acs-armored-combat-shirt/ help protect your arms and shoulders with only a small addition in weight.
Weight and Flexibility
Speed and maneuverability are often as important in a difficult situation as ballistic protection, and you should never forget that.
Although it is possible to use side panels with hard armor, that will lower the rate you turn around and bend, as well as your overall ability to ducks and slide into cover. With such issues, you might become a harder target to injure, but an easier target to hit.
Taking your speed into consideration is essential, as you want to be optimized for the mission. If possible, it is better to remove the possibility of being hit at all than stopping the bullet once it does reach you.