Now, there are varieties types of frame materials, plastic, metal and special alloys. Plastic ones are usually thick but not outdated, and they are spinning back with a fashion today, what’s more, you can choose the color as your wish; while metal ones are durable and light, and if you have a sensitive skin to other materials, stainless steel is a great choice!; bendable titanium frame is a kind of classic alloy metal, they are featuring lightweight and durability, so, kids especially get benefit from such materials, and the price of these products are really cheap at online websites!