This is in no way an official guide and the Factory is in no way obligated to adhere to a strict guideline (I'll reserve my opinions about the consistency of the factory for later). This is just a good generalization of the scale of armor ratings and how, usually, they would be seen in Canon.
[ Class I ]
Leather, Wood, Bone, Conventional Materials
The lightest grade of armor. Commonly made of common materials or sometimes primitive forms of armor. Little if any resistance to blasters and lightsabers (let alone anything). Usually of diminutive weight.
[ Class II ]
Echani Fiber Armor, Spacer's Leather, Blast Vest
Armor commonly consisting of fabrics, padding or kevlar. Light and functional, but still offering decent protection. May have a mild resistance to blaster bolts and similar forms of weaponry.
[ Class III ]
Armorweave, Scout Armor, Count of Serenno Cloak
Typically light armor made primarily for the purpose of protection or combat. Retains a degree of blaster and slug resistance, sometimes mitigating lightsaber damage slightly (as seen with Dooku's cape).
[ Class IV ]
Work in progress (I need to find something from canon to describe this category really well)
[ Class V ]
Vader's Suit, Flex-Armor, Kevlar
True medium-grade armor. Usually made of light alloys or plating. More effective at shrugging off or reducing blaster bolt and slug damages than light armor, but not impervious. Might not be outright rent by a lightsaber but still offers only minor mitigation.
[ Class VI ]
Medium armor made of strong alloys and/or thicker construction. Truly armor made for the battlefield. These types of armor typically offer full coverage and have been known to reduce blaster damage significantly, though heavy (or lucky) shots still seem to punch through on occasion). Again, not outright rent by a lightsaber but not a reliable form of resistance either.
[ Class VII ]
Jedi Knight Armor, ARC Trooper, Shock Trooper, Mandalorian Armor
Medium-heavy armor better still than its predecessor. Armor at this grade generally starts to become cumbersome and somewhat restrictive, but offers substantial protection from gunfire and may help deflect glancing lightsaber blows. Slightly better than standard-issue clone trooper armor, it can take a beating before being rendered useless.
[ Class VIII ]
Eternal Empire Armor, Katarn Commando Armor, Durasteel Heavy Armor
Heavy armor or plate-mail, those who don it standing out distinctly as walking walls. As heavy armor of this nature begins to limit functions on the battlefield, it is usually reserved for specialized combat roles, guard duties or elite fighters. At this rate, may deflect blaster bolts and slugthrower fire to some extent, and would take substantial force to cleave through with a lightsaber.
[ Class IX ]
Beskar'gam, Cortosis Weave, etc
At this point, armor becomes incredibly resistance to various forms of damage and possibly even lightsaber-resistant, taking blows while retaining its integrity. Many exotic and powerful metals such as Mandalorian Iron often fall into this category for their incredible strength or their ability to absolutely minimize damage from lightsaber strikes. Whatever the case, truly protective armor.
[ Class X ]
Matrix Armor, Power Armor
Arguably the best form of protection one can get. Almost certainly restrictive to movement or agility to some extent. This kind of armor may shrug off blaster fire and prevent slugthrowers from causing any penetration, and can take sustained damage before wearing out. In most cases, a lightsaber cannot cut clean through in one try, and in some special cases, not at all.