home made Sun reflector for rear deck

Could make seeing out the back window harder if you leave it there while driving.

 

Whether or not a sunshade "works" is a function of what you want it
to do.

In your case, it would appear you want to keep sunlight from falling
directly on the rear seat and head rest leather upholstery. For that, it
sounds like you found a successful alternative to a full window block.
Good on you.

Yet, there are other reasons for doing the blocking at the glass; one
would be heat buildup in the car.

I was reluctant to get the front and rear window sunshades. I knew
there would be a lot of light/heat pouring into the car with the glass at
such low angles, but I didn't believe a shade would do much good. But
something had to be done. So, I sucked it up and bought the HeatShield
shades from the PriusChat store.

Well, I was wrong.

Coupled with leaving the side windows open about 1/2 inch, they make
a huge difference. The interior of the car is easily ~25 degF cooler.
Sure, they're a minor pain to put in each time when you're running
errands and there's no shade to be found in desert-like parking lots.
And yes, other folks look at you and smirk... little do they know.

It is indicative of the performance of the shades to feel the
temperature difference on the inside and outside reflective surfaces
when you take the shades down. The reflection outward and the ~1/4
inch foam in the center is a winning combination in my experience.

FWIW, putting up the front shade is the more effective of the two as
the dashboard is a real heat sink... cool seats and steering wheel too.

EDIT: I often leave the rear hatch shade in place through multiple
stops. I suspect there is the possibility of a minor legal question here.
But, there are two perfectly usable side mirrors. As to rearward visibility,
I can stii see through the little strip of tinted rear glass. I see it as not
significantly different than having the hatch area full-up to the glass when
vacationing which doesn't warrant a second look from the gendarmarie.

 

Using a sun shade in the front really DOES help a TON. It'll also help the longevity of your dash.

I'm not sure I'd ever really want to get a shade for the back window, unless I had to park outside all day. Fortunately there's a parking garage at work, and I park in the garage at home, so my car will not sit in the sun all day. If it did, who wants to go through the hassle of opening up the hatch and removing the cover?

I'd much rather tint the windows. I plan on doing that when I have some free cash. In past vehicles I've had my windows tinted with nice 3M metallic film, in the darkest shade that is legal in my state... and it is DARK. Combined with a front window shade and cracking the windows just a little, it REALLY makes a difference. On HOT summer days, it can reduce the interior temperature by as much as 30º.