Protection map from the Squad Wiki: coloured by what penetrates, at close range and a neutral angle.

Protection map of "BMP-2" at close range and neutral angle. Shooting from different angles will affect penetration chances. For reliable penetration at most angles aim for "<70mm". Ifv shooting older ammunition (GFI, MEI, IMF, "PLA") may only be able to penetrate "<70mm".
Interactive 3D armour replaces this once the vehicle has been exported from the Squad SDK.