Summer is nearing/here, and it's getting hotter in my house. To save electricity with our super expensive A/C, I constructed reflective curtains to block sunlight from warming our house. Think auto windshield. This is super simple and kind of obvious, but it works well.
Step 1: Materials:
2-3 Emergency blankets/foam reflective pads/ windshield blockers*
Roll of 2" wide tape (I used aluminum tape)
Bag of Grommets and crimper
Bag of curtain hangers
*I don't know about in the US - I've had these before in my camp pack as "emergency blankets" for protecting you in the event of shock or if you have to sleep somewhere in the cold. The emergency blankets don't have any backing on them, so maybe you might want to glue some foam/paper/cloth to the back. Super 77 tack is perfect for this.
I'm currently in Japan, and in the 100Yen shops (great places for makers - come to Japan just to stock up for supplies) they have these mats that are meant to be used as picnic mats.