It is made of plastic, and has two halves which are assembled after the contents have been placed inside it.
the plastic slide switch is used to turn the torch on and off. It has ridges for an easy grip and is a comfortable size for your thumb.
The lens is made of glass. Usually, it is curved to bend the light coming off the reflector from the bulb.
The sealing piece on a torch is mainly to hold the to halves of the torch outside structure together and to protect the lens. It is made of a hard plastic and can easily be screwed on and off if the batteries need changing.
This is effectively a handle, although its main purpose is decoration. It is inserted into the torch's outside she'll and its yellow colour attracts buyers.
the reflector is made of plastic and is used to direct the light from the bulb to the lens. It is as durable as it needs to be for its job, as it is always protected by the lens and the outside of the torch.
This encloses the battery. It is made of the same black plastic as the casing, so it blends in to the handle giving the torch a more whole appearance, and attracting buyers.