FedericoMena

When I started biking I bought a box of tube patches; I think it came with 50 or so round ones that are maybe 5 cm in diameter, and they feel a good 1.5mm thick. I haven't used them all up yet. I carry a few in my toolkit, along with sandpaper and rubber cement.

One day my LBS owner, an old and cranky ex-racer, looked and my toolkit and complained at those ugly patches. Too big, too fat, he said. So he gave me a 10x10 cm square of a thin rubber patch sheet. Cut up a little bit each time you need it, he said.

I love it. I can make patches that are about 1 cm square, and they are thin and pretty. I've been going through the sheet, one little bit at a time, and it's just so nice. I don't have skinny tyres or anything, but these work so well!

Why do patch kits come with huge and fat patches, anyway?

DrIsotope

The patches in my kit are about the size of a US dime-- 18mm or so. I've not personally seen larger.

Plimogz

I have on occasion used a large patch out of one of the kits I had purchased to repair both punctures on a snake bite. I have also used a larger than usual size to patch a centimeter-long gash from a particularly nasty road debris. However, for the majority of flats, when the puncture is basically a pinprick, the smallest patches get the job done just fine.

As to thickness, I have come across thicker, less compliant patches in some cheaper kits; these tended to deform the tube more after repairs. But I have not had any problems using patches similar to the one sold by Rema -- similar in thickness, not necessarily with the nice feathered edges.

Whatever works well for you and reliably gets you back on the road

Andrew R Stewart 

Could the thick patches be from the auto world. Years ago I watched an old time mechanic patch my auto's tire using a similar patch. He used a wire wheel on a hand drill to buff the inside of the tire casing before layering glue then the patch. I suspect he could have taught me a few things if I hung around more. Andy.

Bill Kapaun

The feathered edges of REMA patches allow you to overlap patches easily. You can't do that with thick edges.
I'll pay a bit more for a patch that has always worked for me.

noglider 

I don't know for sure, but I assume they make patches thick in the middle not because we need them to be thick but so that they can be thin at the edges. I suspect this tapered edge helps keep the patch in place.