Sepang is a very difficult track on the Formula One calendar, its offers a long straights and some tight, twisty corners where a good aerodynamic package is crucial. But as often seen in the past teams have slimmed their wings for better straight line speed.
Ferrari
On the rear mainplane of the SF15-T Ferrari used Flow-Viz aero paint to monitor the streamlines that come over the central section and then over the wing. The paint will show flow markings on where the airflow is being directed. This is an important aerodynamic understanding on how to improve the car’s efficiency. Where you have too much curling lines you have too much turbulence and thus lose downforce from it. 
Williams
Williams brought a couple of pieces to Malaysia. They increased the on the lower section of the engine cover. This is above the radiators mounting points of the car, which means more heat can be extracted from the radiators and PU. The hot climate with Malaysia plays havoc with cars cooling systems, so they implemented extra louvers to cope with the engine heat.
Red Bull
Red Bull continue to argue with Renault over the PU issues they currently have. Red Bull have taken away the rear wing endplate elongated louvers which creare a pressure gradient between the coefficient high and low pressure.
McLaren
McLaren finally have the driver line-up they wanted, as Alonso is now back in the car after his injury during testing. On the front nose section you can see they have implemented a new S-duct system on the car. The S-duct works by air entering under the T-tray under the bulkhead. Air enters here and exits where the top outlet where the air pylon once was. The way the S-duct is a “S-shaped design which increases the rate of high pressure air over the top of the car, so is not being wasted going under the car.
You gain a vortex above the car so that its can help to push the car into the road, when it hits the rear wing.
Images Courtesy of Williams F1 Team, Scuderia Ferrari and Mercedes AMG F1 Team
