Cat MateLarge 4-way Cat Flap Brown

Q: Is the cat door see through transparent like glass or opaque, my cat will not go through unless she can see what is behind the door

It is very clear, transparent, like glass. Not opaque (my old cat door was probably what you call opaque, like a haze or film over it; this is definitely clear in comparison).

Q: Will this work in an alluminum storm door? Our cat is 16 lbs will it accomodate his size?

The unit may stick out depending how thick the aluminum door is. I have it in a inside wooden door at a thickness of an inch and a half. It should work but it may not be flush on both sides. I would try though. As for the cat size, I've got 2. 20 / 21lb maine coons , they walk right through with no problem whatsoever. The only door I was able to find to accommodate large cats. Again, I would buy and try. Scot

Q: What are the exterior dimensions of this pet door.???

9"wide x 9.5" long. That's the frame exterior. It works great! I have it on an inside door to my bedroom. I can lock them out when I want to sleep. Or let them come in for morning cuddle time.