are you talking about the frame?
the main frame of a scooter can be made from several types of materials,
Strong Steel Alloy Plated with crome
Aluminium Alloy
(just do a google search under fold-up scooter material.. .. or go to company websites for razor or blade and they'll have a product information.. about the device is made of.. etc etc.. they'll also have some type of objective for that item -- why they designed something like that etc etc
even still go into a bicycle shop -- some of the dudes in there are pretty helpful ")
Design Considerations
when you are designing such a product you must look at the following properties
think of it: what is their main objective, who are the target audience? How will this be used? also put in mind how much the device might cost ( not necessariliy .. but in some cases money is an issue --which can lead to the descisions by the company of what materials they would use, packaging, labouring costs etc etc..
since as you said it's a fold-up scooter, it must be portable - light, small, tough
from there we can deduce how big, small the device is, calculate the types of materials that could be used, (whether it has the required propertiesor not)
i can't think of anything else.. and i better get back to work
hope that helps!