Hydrogen bonding is stronger than London dispersion forces due to the nature of their interactions and the specific conditions required for each to occur. Hydrogen bonding is a specific type of dipole-dipole interaction that occurs between a hydrogen atom covalently bonded to a highly electronegative atom like nitrogen, oxygen, or fluorine and another electronegative atom. This interaction is relatively strong because the difference in electronegativity between hydrogen and the other atom creates a significant dipole. In contrast, London dispersion forces are induced dipole-induced dipole interactions that occur between all molecules, regardless of their polarity. These forces are the result of temporary fluctuations in electron distribution that induce temporary dipoles, resulting in a weaker, transient attraction. Therefore, the permanence and dipole strength in hydrogen bonds make them stronger than the fluctuating, weaker London dispersion forces.

Waterproof materials are designed to prevent water from passing through, essential for various applications from outdoor clothing to construction. They can be made from rubber, plastic (like PVC or polyurethane), silicone, and treated fabrics (such as those coated with a waterproof membrane or laminate). Rubber is naturally waterproof and used in products like rain boots. Plastics, due to their impermeability, are used in rainwear and waterproof covers. Silicone coatings are applied to fabrics to repel water. Treated fabrics, through technologies like Gore-Tex, involve a membrane that blocks water from entering while allowing vapor to escape, making the material breathable and waterproof. These innovations showcase the integration of material science and technology in creating effective barriers against water.

High Density Polyethylene (HDPE), not Polyvinyl Chloride (PVC), is often discussed in terms of density and scratch resistance. HDPE can indeed be scratched, though it is known for its durability and resistance to impact. The material's scratch resistance is not absolute and depends on the force applied and the object's hardness causing the scratch. While HDPE possesses a high level of resistance to many forms of physical damage, it is still susceptible to scratches under certain conditions, especially from sharp or abrasive materials. For applications where scratch resistance is critical, additional surface treatments or more scratch-resistant materials might be considered.