The main way to make the bicycles light is do the buttering for the frame.Also have the light parts to match.

Do you know how to Butting?Please look at that.

"Butting"

To increase strength without adding extra weight, frame builders use internal tube 'butting' on chromoly and aluminium tubes. The more butting or intentional variation in tube wall thickness the higher the cost: a result of greater complexity in the manufacturing process.

• Straight gauge tubing is the same thickness for the length of the tube.
• Single butted tubes are thicker at one end, like the seat tube which is thicker at the bottom bracket junction.
• Double butted is thinner in the middle than either end where the tube is joined or welded.
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• Triple butted takes the next step with three variations in tube wall thickness. 
  
  Firstly,company must have these process:
  
  1. hydroforming
  2. mechanical shaping
  3. taper-butting
  4. double-pass smooth welding
  5. heat treating
  
  Secondly,the strength must be stronger.Generally,good quality alloy butter can be light to 1kgs,like 7075,also need to add a new material together.Through many tests.
  
  
  Can you estimate these folding bikes weight?It is 11.6kgs.Of course,the lightest material must depends on Carbon.But it is expensive.So if you want to the light and cheap bike,the important progress is butted for frame. Ok,let's do that.