Experimental results on the acoustic properties of aerogel/fiber composite materials and polyester 100% nonwovens are presented. The effects of the thickness, combination, and solidity of acoustic absorbents on the sound absorption coefficient were investigated. The capacity of sound absorption was measured by ISO 10534-1:1966. At a thickness of aerogel/fiber composite materials of 18 mm the coefficient of sound absorption reaches values of more than 70% for 630 Hz. With increasing thickness of the aerogel/fiber composite materials, the maximum value moves towards lower frequencies. The polyester 100% nonwovens exhibit high coefficient of sound absorption in the high frequency range with increasing thickness and solidity. Multilayered stacks(combinations of aerogel/fiber composite materials and polyester 100% nonwovens) can take advantage of high attenuation in both low and high frequency ranges. The experimental determination of the characteristic attenuation for each acoustic absorbent allows us to determine the acoustical characteristics of multilayered stack and could lead to an optimization of the number of layers and of the thickness of each layer for a given combination.