The ice layer is 1/16th of a block, with the texture of packed ice.
It can be walked over normally, and will eventually melt away. It can be placed on any face of a normal block, and can be stacked, allowing the creation of a full block.
If exploded, blocks with an Ice Layer on any of its 6 faces will have their blast resistance ignored. This means that for example Obsidian can be destroyed by explosions if covered in ice.