Hey, guys I am about to make an underquilt/cover for my GTUL.

I'm going to be using a poncho, an emergency blanket, and a thin fleece blanket.

I'm looking to add 1 more thin, cheap, and insulating layer that is common (so I do not have to order it; Something that can be bought from the dollar store, target, or sears).

Everything has been free so far because I received everything as a gift or free. For reference if anyone wants to make something similar, the fleece blanket is about 10-12 dollars, the poncho was about 4 dollars, and the emergency blanket can be anywhere from 5-15 dollars.

I don't have shock cord. I will try to find some but if I cannot find any does anyone know of some knots between 2 sections of cords that lengthen when tension is applied?