Abstract: Various combinations of retroreflective sheeting and multilayer polymeric reflective films are disclosed. The reflective film includes alternating layers of at least a first and second polymer, the alternating layers being configured to exhibit a high reflectance for light within a first spectral range and a low reflectance for light within a second spectral range. At least two of the alternating layers can have out-of-plane indices of refraction which differ by no more than 50% of the maximum in-plane refractive index difference. The polymeric layers can define optical repeating units arranged in a sequence to have a specific thickness profile designed to give sharpened spectral transitions. The retroreflective layer preferably exhibits retroreflectance in all planes of incidence, but alternately it can be retroreflective in at least one plane of incidence but not in at least one other plane of incidence.

Abstract: Retroreflective cube-corner articles having randomly oriented cube-corner elements exhibiting rotational symmetry and entrance angularity like microsphere-based sheeting but having increased retroreflective efficiency from cube-corners. The inventive sheeting may contain cube-corner elements typically of different cube-corner geometries, different cube-corner dimensions, and different central axis heights. The cube-corner elements are positioned randomly and are typically not adjacent to one another. Also, methods of making such articles are provided.

Abstract: Procedure for making Al.sub.2 O.sub.3 spheroids, 600 micrometers in diameter or less, utilizes an AlOOH sol containing 0.25% weight percent MgO (in the form of Mg(NO.sub.3).sub.2 .multidot.6H.sub.2 O) and HNO.sub.3. The sol is dispersed into droplets in a particle forming fluid (e.g., 2-ethylhexanol) where gelling occurs. The gelled spheroids are collected, dried and pre-fired in air at temperatures less than 1,200.degree. C. for up to about 12 hours. The dried and prefired beads are fired in a 2-step process at temperatures of about 1,850-1,950.degree. C. in the following sequence:a first dry oxygen firing for about ten minutes, followed by a wet hydrogen firing for up to 350 minutes. Reasonably transparent microspheres having crystallites in the range of 5-100 micrometers are obtained with little intergranular porosity, and their density is estimated to be near theoretical.

Abstract: Glass microspheres and other glass elements based on B.sub.2 O.sub.3, BaO, SiO.sub.2 and TiO.sub.2 have an improved combination of crushing strength, index of refraction, and, especially in some formulations, chemical resistance. The microspheres are especially adapted for use as retroreflective elements in pavement markings.