Thickness does not necessarily equal strength. There are many other factors from materials to manufacturing techniques that come into play. High quality Japanese manufacturers, such as Bomex, prefer thin, light weight Fiberglass. This thin Fiberglass is not fragile or cheap like some low quality no-name-brand kits out there. Some of the cheap low-quality kits are made of thick strong Fiberglass. This can be a disadvantage as the overly rigid part is harder to install, especially if the fitment is even slightly off.
I've delt with thick Fiberglass kits before... its NOT fun
...if the fitment is slightly off, it wont bend into correct position, causing the kit to look cheap