hydro shops should be a good source... I have bought some pretty nice stuff from edmund scientific over the years... and their description of mylar sounds a lot like the blankets, and if you look at the pic carefully you will see the same size creases
Mylar Reflective Film Sheeting
Mylar – History and manufacturing
DuPont developed Mylar in the mid-1950s. In 1960 and 1964 NASA launched the Echo satellites, 100-foot diameter (30M) balloons of metallized 0.005 inch (0.13 mm) thick Mylar film.
In manufacture, a film of molten PET is cast on a roll and subsequently stretched orthogonally to the direction of travel. One side is normally microscopically smooth, while the other side contains microscopic asperities, which promote adhesion of coatings and printing media.
Mylar can be aluminized by sputtering a thin film of metal onto it. The result is much less permeable to gasses (important in food packaging) and reflects up to 99% of light, including much of the infrared spectrum. Like aluminum foil, aluminized Mylar has a shiny reflective side and a dull side. Mylar does not tear easily, unlike tin foil and aluminum foil.
Metallized nylon (or "foil") balloons used for floral arrangements and parties are often mistakenly called "Mylar". Many museums, archival institutions and those in the collecting areas of currency, stamps and comics use Mylar to protect their collectibles from damaging light rays.
In addition, farmers and hydroponics enthusiasts employ Mylar in their craft because the highly reflective nature of the film increases plant growth and yield by 35% or more.
Useful as an insulating material to reflect away heat and/or light, and as a light filtering element. Pkg. of 2.
Specifications:
* Thickness: 0.5 mil
* Dimensions: 56" x 84"
* Reflectance: 90%; 0.4 to 15 micron range
* Transmission: 10%; 0.4 to 15 micron range
* Mylar Sheeting (Pkg. of 2)
item number: 3053604 Mylar, Blanket Sheeting Pkg/2 56" x 84", Reflects 90% Of Body Heat Back, Weight 2oz
edit: but given the choice of creases or no creases well... thats a no brainer