I am the "proud" owner of these cheap earmuffs. I was thinking the other day what could I do to enhance their performance.
Their materials are really cheap and flimsy, to bring down the production cost. They were bought for 2.5 Euros.
I mainly use them at the workshop when cutting and grinding or at outside noisy activities like wood cutting with a gasoline wood-saw.
Step 1: Remove the Old Insulation
I don't have actual footage of the old insulation because it was discarded. It was nothing more than a small piece of ordinary foam (like the black foam in the picture) which wasn't occupying a lot of space in the cavity.
To hold it in place the manufacturer added another piece of thinner foam (3 mm in thickness!) to seal the cavity. You can't go cheaper than that, unless you install no insulation at all!
Step 2: New Insulation
I had some foam material in my inventory which had the correct size for the project.
I used one blue cubic foam piece per side.
Step 3: Finished
I noticed a sufficient improvement after the hack. I am aware of the low end abilities of the apparatus and I am considering investing in a better model. I think something in the range of 35-37 nrr (noise reduction ratings) will do.