Stainless steel 316L (Stainless Steel) is a very durable material that theoretically can not be destroyed. It is hard (non-bendable and non-crackable), color stable, antiallergic (does not react with body fluids and therefore no metal components are not released into the skin and flesh) and has anticorrosive surface (the surface is resistant to oxidation and corrosion. Moreover, it is also resistant to fresh and salt water).
Watches marked with water tightness 30M/3ATM are designed for incidental contact with water (car wash, rain). 30M/3ATM indicates the degree of water resistance standardized by ISO 2281. ISO tests include temperature changes, depth, pressure (water and air) for different times under rest during manipulation with the operative part of the watch.
Sapphire glass in the watch was made in a laboratory by melting aluminium oxide (Al2O3) in the presence of hydrogen and oxygen at 2000 °C. After crystallisation into the corundum 'pear', it's cut and further processed into the desired shape and size. Sapphire glass is the hardest glass used in watches. It would be second behind diamond on the scale of mineral hardness, so it can only scratched by diamond. Its only disadvantage is its fragility.