I think you're referring to the MLI used on the ISS. Here's a layman's explanation of MLI:
Staying Cool on the ISS - NASA Science
The gold color you are referring to is likely the kapton film. NASA uses many types of thermal blankets though. But like others have said it doesn't magically absorb the heat, it either reflects radiation or limits conduction or both. If you really want to blow the bank you can coat the inside of certain key engine and exhaust components with TBC's (thermal barrier coatings) and low friction coatings.