There are currently 3 X-mount lenses with “WR” in the product name.
XF16-55mmF2.8 R LM WR
XF50-140mmF2.8 R LM OIS WR
XF18-135mmF3.5-5.6 R LM OIS WR
To be able to use under severe condition, sealing has been applied in various parts of the lenses, but sealing ins’t the only technology that make the lenses “WR”. Air Ventilation is another technology that plays an important role.
The volume of the inner barrel changes for lenses such as XF16-55mm and XF18-135mm, which extend the overall lens length when adjusting zoom. It means that the air moves inside the lens barrel.
Smooth air movement is needed for smooth zooming operation, but as the clearance has been removed to the utmost limit to make lenses dust-resistant and water-resistant, there isn’t much space for air to move freely inside the lens barrel.
In order to solve the problem, a ventilator is placed in the interior of the bottom of the lens barrel. The structure effectively prevents dust particles and moisture from getting into the lenses to allow for smooth operation. Technologies, that are not so obvious, create help making the lens “Weather Resistant” as written at the bottom of the lenses.