Any advice as to what this might be on my front brakes?

Technical Area Wheels, Tyres & Brakes
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  1. My model of MX-5 is: __2012 PRHT 2.0 Venture Edition
  2. I’m based near: __Sheffield
  3. I’m looking for technical help or recommendations on: __Front Brakes

Just spent an afternoon working on my 5 and noticed what looked like some kind of paper or cover on the inner edge of my brakes.
It appears to be on both sides but only the fronts and not the rears

Not sure what it is, thought I might have picked up some rubbish at first but whenI saw it was on both fronts I decided against trying to pull it out to remove it

I have driven quite a few vehicles over the years and never seen anything like this.

Any advice would be appreciated.

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2

Masking tape from when the calipers have been painted?

3

Looks odd, I’d be taking them apart for a proper look or at least picking at that stuff.

4

A very poor homemade anti-squeal?

5

Thanks for the advice folks.
I will try and get a good look at them when I get the chance.
The calipers haven’t been painted since we got the car in June 2020 but on closer inspection of the photos I suppose they could have been painted a grey colour by a previous owner.
Sorry to admin about the duplication of the question in the area section, didn’t realise.