It's not the new aluminum alloy material that causes the new iPhone flagships to weigh heavier. The added weight is actually based on the phones' new technology.

The said technology is actually the new 3D Touch that Apple's been touting on its new iPhones. According to Apple, 3D Touch in the latest iPhone devices makes the phone easily respond to subtle taps. It introduces the so-called Peek and Pop in addition to the phone's other familiar Multi-Touch gestures such as Pinch, Tap and Swipe.

"Not only will you see what a press can do - you'll feel it," said Apple on its official site.

Apple has integrated 3D Touch into the phone's display assembly. As a result, the display assembly has become twice heavier than before. The display in the iPhone 6 is said to weigh 12 grams (0.026 pounds). With the new 3D Touch, the new iPhone 6s display now weighs 29 grams (0.064 pounds).

The added weight is attributed to the new layer that Apple has added to the display assembly  for the phone to have the ability to measure the amount of pressure. Apple reportedly equipped the backlight of the display with a new capacitive pressure. In addition to the new weight, the screen also seems to appear a bit thicker than usual.

"Using 3D Touch is simple," said Apple. "But the engineering behind it is incredibly advanced. When you press the display, capacitive sensors instantly measure microscopic changes in the distance between the cover glass and the backlight. iOS uses these measurements to provide fast, accurate and continuous response to finger pressure, which could only happen with deep integration between software and hardware."

Another reason for the added weight is Taptic Engine which, according to Apple, allows the phone to give real time feedback based on the user's subtle taps on his device.

"These responses correspond to how deeply you're pressing the display, and they let you know what actions you're performing and what you can expect to happen," said Apple.

Overall, the new iPhone 6s and iPhone 6s Plus are said to weigh 14 and 20 grams (0.031 and 0.044 pounds) heavier than their respective predecessors. The iPhone 6 tips the scale at 129 grams (0.28 pounds) while the iPhone 6 Plus weighs 172 grams (0.38 pounds).