When Apple took the wraps off the totally redesigned iPhone 6 and 6 Plus last September, some huge differences between the new phones and previous iPhones were immediately apparent.

The screens on the new phones were bigger than those on any previous iPhone. The phones were also thinner and lighter.

But most notably, unlike earlier iPhones, which had panels on the back made of ceramic and glass, the case of the newest iPhone was made entirely of aluminum, save for some thin, plastic-like lines that run across the phone at the top and bottom of the device.

The lines are white on the gold and "rose gold" iPhone models, and gray on the silver and "space gray" models. 

Those strips are a source of consternation for some people, who've vented about their presence on Twitter. There's even a discussion thread on the question and answer site Quora that asks if Steve Jobs would ever have allowed the phone to have them. (Answer: nobody knows).

Apple wouldn't tell Tech Insider the purpose of the white lines, though the consensus among company observers is that they have something to do with the iPhone's antenna or signal.

iphone 6s skitchApple/Tech InsiderApple's latest iPhones.

To learn more, we reached out to Jeff Snyder, the director of marketing at iFixit, a company that sells tools and parts and provides repair guides for people for how to fix their gadgets. iFixit is also known for doing teardowns — taking apart and posting the pictures — of new gadgets. 

Here's what Snyder said about those lines on the iPhone:

We believe that the lines/bars on the outer case provide a clean escape route for the signal to get through the case.

The iPhone 5 and 5s had glass sections on the back, both top and bottom, for the same reason—and the iPhone 4 and 4s had glass backs. 

Apple is likely looking into ways to eliminate this design feature from future iPhone models. The company filed a patent earlier this year for a composite material that will allow radio signals to escape.