Acrylonitrile butadiene styrene back cover with rounded edges http://www.bpf.co.uk//innovation/Plastics_in_Electrical_and_Electronic_Applications.aspx - to keep the product child safe and is an insulating material so the user does not get electrocuted if a fault develops in the circuit. Product is comfortable and easy to hold so is ergonomically produced.
Silicone button base - to make the buttons easier to touch for the ergonomics of the product. They provide a definitive touch to the product and shows the user that they have touched the buttons, to give the correct sum on the calculator.
Electrical circuit https://en.wikipedia.org/wiki/Calculator#Power_source - to power the product through the on and off buttons. Also includes solar panels for 2 - way power. Wiring made out of copper, as that material is a good elictrical conductor. Copper is flexible and can also be easily changed into the wire shape. The wiring would then have a Melamine formaldehyde cover as it is an electrical insulator and will prevent electricity caused injuries. http://www.bbc.co.uk/schools/gcsebitesize/design/resistantmaterials/materialsmaterialsrev3.shtml
Screws - made of steel and are small to make the aesthetic of the product more desirable. The steel used is usually high carbon steel as it is hard and not easily breakable. The sustainability of this material is good because steel can be infinitely recycled and doesn't have a huge impact on the environment.
Acrylonitrile butadiene styrene front cover with rounded edges - similar to the plastic back cover, this is to make sure that the product is safe for children and comfortable to hold (ergonomics). This material is malleable and easy to change and form to your desire. The cover has cutouts in the needed areas to make space for buttons and solar panels.
High density polythene buttons
http://www.bbc.co.uk/schools/gcsebitesize/design/resistantmaterials/materialsmaterialsrev3.shtml - made of this material as it is hard and stiff for the buttons unlike the rubbery button base. On the buttons written in permanent paint is numbers and mathematical statements. The paint can be easily scratched and by the end of this product's life, the numerical values and mathematical statements may not be visible anymore. Each button may have a different shape to another and are different sizes as well.