I need some help here.......I am making curtains for a west window and I am wanting to put a thermal barrier between the inside curtain fabric and the outside lining. The only thing I can think of is those cheap metallic "space blankets." My local fabric store was no help and neither was Google. So........

Does anybody know if I can
1) Sew a space blanket (will it just come apart on the stitch line?)
2) What happens if I launder a space blanket? (Obviously, I could not use very much heat to dry it......just a few minutes on low heat, then hang and hope the wrinkles fall out.....)
3) Any other yard goods suggestions for keeping west summer sun out and heat in during winter?