Materials
Materials are properties all Roblox parts have, changing both the physical and visual characteristics of a part. These physical properties are somewhat useful for shredder armor and blades.
"For example, concrete is heavier than plastic and sinks faster in water. When you set the material of a part or terrain, Roblox simulates its physical material properties to make this behavior just work." https://create.roblox.com/docs/parts/materials
Physical Properties
Materials have several physical properties, including elasticity, friction, density, and their associated weights. For shredders, elasticity and friction are generally the most relevant.
Elasticity
Elasticity determines how much a part bounces when it collides with another object. Higher elasticity can help armor deflect incoming blades, reducing the force transferred toward the core.
Materials with the most elasticity are default, smoothplastic, and fabric.
Friction
Parts with lower friction slide more easily against other surfaces. As a result, blades with lower friction values generally experience less resistance and can achieve greater penetration force.
Friction is generally less important for armor than for blades, and the practical difference between materials is often small.
The material with the least friction is ice, at 0.06.
E/F Weights
Friction Weight and Elasticity Weight act as multipliers on a material's base friction and elasticity values. For example, Ice has a friction value of 0.02 and a Friction Weight of 3, resulting in an effective friction value of 0.06. If you'd like to read up more on this check the offical roblox developer doccumentation for friction weight and respectfully.