The material itself is highly porous.
Do foam gutter inserts work.
In fact gutter guards are extremely useful in many ways.
It is designed to allow the pores within the sponge like material to let water pass through to your gutters and down your downspouts.
Foam filters employ the principle of displacement there is nowhere for the debris to go because the gutter is mostly filled with this material.
As a result debris gets trapped at the surface of the foam.
Inserts have proven to do a very solid and affordable job of keeping debris out of gutters and are effective with a wide spectrum of debris from needles to leaves.
Sponge gutter guards are a do it yourself product and can be found at most home improvement stores.
Most sponge gutter guards consist of an open cell polyurethane insert or an insert made of foam.
They only cost you about 2 per feet.
This foam or sponge acts as a trap by intending to filter any large debris out of the water that flows down the gutter.
However a foam gutter guard collects water just like a sponge and often times becomes trapped within the guard.