Acoustical will be the main sealant used on polyethylene (air/vapour retarder). It needs to be sandwiched between two surfaces in order to create a seal. When using a black acoustical product between polyethylene sheets, the acoustical should appear black, letting you know it has sealed properly. When the acoustical is not in contact with the outer polyethylene sheet, it will appear to be a grey colour, this usually indicates that it is not sealed properly.

Tip: Acoustical sealant can be very messy to work with and difficult to remove from skin and clothing, but naturally adheres/sticks to vapour retarder. Tools can be cleaned with DW-40 or Kerosene.