While data varies on
ear plug style, this is mainly a chart on a material's effectiviness.
+-------------------+-----+--------------------------------+------+------+------+------+------+------+------+------+
| Ear plug material | NRR | Frequency (HZ): 125 | 250 | 500 | 1000 | 2000 | 3150 | 4000 | 6300 | 8000 |
+-------------------+-----+--------------------------------+------+------+------+------+------+------+------+------+
| Soft Silicone | 21 | Mean Attenuation dB: 25.1 | 24.0 | 22.3 | 26.5 | 36.0 | 41.0 | 40.8 | 40.3 | 40.3 |
| | | Standard Attenuation dB: 3.8 | 3.5 | 3.0 | 3.1 | 3.5 | 3.8 | 3.8 | 3.3 | 3.0 |
+-------------------+-----+-------------------------+------+------+------+------+------+------+------+------+------+
| Soft Wax | 24 | | 23.0 | 24.5 | 25.6 | 30.1 | 35.6 | 40.8 | 40.0 | 39.0 | 40.0 |
| | | | 3.2 | 3.0 | 3.0 | 1.8 | 2.4 | 1.7 | 2.6 | 3.3 | 4.0 |
+-------------------+-----+-------------------------+------+------+------+------+------+------+------+------+------+
| Soft Foam | 33 | | 33.1 | 36.3 | 36.8 | 38.4 | 38.7 | 44.1 | 44.1 | 45.4 | 46.0 |
| | | | 2.7 | 1.8 | 2.1 | 1.7 | 2.1 | 2.3 | 2.3 | 2.2 | 2.4 |
+-------------------+-----+-------------------------+------+------+------+------+------+------+------+------+------+
| Low Pressure | 30 | | 33.5 | 33.6 | 36.0 | 37.5 | 39.4 | 42.5 | 42.5 | 43.7 | 45.2 |
| | | | 3.6 | 3.4 | 3.2 | 3.5 | 3.5 | 3.4 | 3.4 | 4.8 | 5.1 |
+-------------------+-----+-------------------------+------+------+------+------+------+------+------+------+------+
All according to
ANSI Standard S 3.19 (1974)