Originally Posted by S~Factor

You can have the best of both worlds. Strength and stiffness of aluminum and the look of a 1/4" abs by gluing a strip of 3" aluminum to your ABS sides splitters to prevent warping.

I, however, do not recommend relying on double sided tape to mostly hold the splitters. When I install them I use no less than 7-8 screws spread out evenly.

This is a picture of what I've done on a e90/92.