Why use Gtechniq Crystal Serum Light overcoated with EXOv4 Ultra Durable Hydrophobic Coating? Crystal Serum Light is an excellent DIY, stand-alone coating offering unparalleled gloss and gloss retention through its superb resistance to wash swirls. However, its water repellency falls short of what EXO has to offer. Therefore, if you want the best for your car – remarkable swirl resistance and water repellency, then this kit certainly is for you. You can save 20% when buying this kit, in comparison to buying each product separately. Storage and Use: Apply Crystal Serum Light first following the instructions from the Crystal Serum Light web page. Once applied you can, without waiting or needing to use Panel Wipe, apply the EXO directly over the Crystal Serum Light. We recommend you apply EXO to your vehicle's panels in the same order you did when applying the Crystal Serum Light. And as with the CSL please follow the instructions from the EXO web page.