I purchased ten Mylar blankets from Amazon for under ten dollars. They are thin but tough. I will be replacing these with more substantial Mylar Space Blankets from Walmart as soon as they are back in stock. (See photo.) They cost $8 at Walmart and $18 at REI. They appear to be two layers and have grommets, which will make hanging them much easier.
I draped the cheap ones loosely around my plants in the GH last week when the temperature went down to 42. I turned on a 65-watt incandescent lightbulb at floor level, and a small fan. The low temperature in the GH was 53 degrees --- a whopping 11 degrees warmer than outside. This was due to the blankets reflecting the heat back onto the plants. When it gets colder (usually not much below 28 in Central Texas), I will use two bulbs. I will utilize the nicer space blankets once they are back in stock at Walmart. Note: I have used GE Silicone II around all of the panels and that helps to raise the temperature a degree or two.