As someone who has been wearing earplugs for decades for motorcycles, firearms and other loud events, this information at face value is a bit off.

Foam by far has the most effective NRR. Silicone and wax are fine but will not provide as effective of NRR. That said, if it’s for sleeping silicone and wax are probably fine. I would argue that foam is not scratchy at all but I usually buy more expensive brands like Mack’s and it’s good to try out different sizes.