This is the model miniature Kane shroud that is seen being fired out into space from the Nostromo after Kane's violent "chestburster" death.
It is made from resin which then has individual tape wraps to complete the detailing (they can be spotted in the "close-up of ejection scene" image posted here). There is a piece of armature wire still attached to the feet of the miniature which was hooked up to a line for filming the scene.
There is some very faint grey / black paint detail on the miniature showing the window in the shroud and the other strapping. These painted details match rather well the ones seen on the full size shroud. This version of the shroud was only glimpsed on a monitor screen when Dallas presses a key to initiate its ejection into space. (the full-size shroud was initially made because, if we refer to Ridley Scott's storyboards, it was supposed to be seen orbiting around the Nostromo at some point in the film… but that's another story !)
This miniature came from a member of the production team at Shepperton and was gifted to him by one of the SFX guys after filming wrapped up.
The model is in overall good condition, with minor scratches here and there.