New images of the purported iPhone 6s Plus expected to be released by Apple this September have made their way online, and they hint at small changes that could have big effects for Apple's upcoming big-screen smartphone.

The images, which were leaked by website Future Supplier, do not show a lot of difference between the rear housing for the iPhone 6 Plus and the rumored smartphone. On the outside, it could be easily mistaken for Apple's current flagship. However, the changes are seen mostly on the inside, or they cannot be seen at all.

The noticeable change is the placement of the two screw holes on the inside of the housing, which are located slightly higher than the screw holes on the iPhone 6 Plus' housing. This suggests that Apple might be planning to use a different loudspeaker for the new device.

Future Supplier also says Apple will change the material of the rear housing altogether, which means Apple could likely be trying to stay away from another episode of Bendgate, where many iPhone 6 and iPhone 6 Plus users reported having their iPhones bending in their pockets.

"The iPhone 6 Plus' rear housing feels smoother than the iPhone 6s Plus, while the 6s Plus' rear housing is stronger," says a source cited by the website.

This appears to be in line with earlier reports that the iPhone 6s and iPhone 6s Plus will be using a much stronger aluminum alloy for the housing of its new iPhones in place of the current aluminum alloy on the iPhone 6 and iPhone 6 Plus. KGI Securities analyst Ming-Chi Kuo, a respected Apple analyst, says the new iPhones will likely use aircraft-grade 7000-series aluminum that will keep the phones from bending or warping throughout their entire lifetime.

Kuo also suggested that the upcoming iPhones will come with a rose gold-colored housing similar to the rose gold 18K option for the Apple Watch Edition. It is also possible that Apple might release a similar luxury 18K gold iPhone for the extremely rich.

More importantly, Apple is said to be a new System in Package (SIP) technology and a Printed Circuit Board (PCB) as a transition before completely getting rid of the PCBs for the iPhone 7 and iPhone 7 Plus. Using SIP frees up some space on the inside of the phone, which can be used for a bigger battery.

Check out the images below to have a look at the purported casing for the upcoming iPhones.