in my friends back yard at dusk, sun was setting but there was still plenty of light, 4 people saw an object. It was larger than a balloon though one witness felt it was a mylar balloon. Seemed more proportional to a small car, was black or dark in color reflecting the sun in the body at one small area which showed it as a flat plane where the reflection was. It did not tumble like a balloon or float, it has a very constant speed, about 30-40mph and traveled in a distinctly straight line towards the Van Nuys airport. Then when approaching the airport it changed course slightly but directly to travel north out of the perpendicular path of the runways.The reasoning behind reporting this is:1. the speed the object was moving was consistent and faster than a car and never changed though there was no lower wind blowing that evening.2. the object did not tumble or have weightlessness like a balloon and was close enough to make apparent it was NOT a heli or plane. There was no noise.3. it rotated slowly on its y axis(y is up) to reveal the setting sun as a reflection on its 'planar' side then held that position4. when it changed direction it was distinct, but kept a straight line as previously was being traveled. It was traveling straight and level, with a decent clip of speed. It never went up or down in altitude, never slowed, and only rotated about 30degrees on the y axis then stopped rotating. 5. there was nothing like string or lines hanging from below it, nor was it a grouping of traditional round or sphere like balloons and if it was mylar I would expect the reflection we saw would have been all over its side. As it rotated on its y axis from what looked like a planar surface to another planar surface that is when we saw the sunset reflected on it. we are not sure what it was, but it had control of its own altitude, speed and trajectory which was moving an object of substance and weight with little effort.