---
title: "Sound insulating materials"
subject: "Civil Engineering Materials"
chapter: 10
key: "semester_3/civil_engineering_materials:sound-insulating-materials"
source: https://www.bctengineer.com/q/semester_3/civil_engineering_materials/sound-insulating-materials
site: BCT Engineering
---

# Sound insulating materials

Civil Engineering Materials · Chapter 10: Asphalt, Bitumen, Tar and Miscellaneous Materials

- Asked in: 2080 Bhadra, 1 marks; 2080 Baisakh, 2 marks (asked 2 times)
- Video: [Heat Insulating Materials & Sound Insulating Materials | Properties | Construction Materials](https://www.youtube.com/watch?v=rAj4fi6yZ4U) — Polytechnic Class (READBY) 
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/civil_engineering_materials/sound-insulating-materials
- Whole chapter: https://www.bctengineer.com/md/semester_3/civil_engineering_materials/chapter-10

## Question

Define sound insulating materials. Write the requirements of sound insulating materials with examples.

## Short answer

Sound insulating materials reduce noise transmission or absorb sound. Requirements: porous for absorption (e.g., acoustic tiles, glass wool), dense for blocking (e.g., brick walls), high absorption coefficient, fire- and moisture-resistance, durability. Examples: mineral wool, plasterboards, rubber pads, carpets.

## Answer

#### Definition

**Sound insulating materials** are materials used in walls, floors, ceilings and partitions to absorb sound energy or stop its transmission, so that noise from outside or between rooms is reduced and a room has good acoustics.

#### Requirements

1. **Porous and light (for absorption):** Sound enters the pores and is changed to heat.
2. **Heavy and dense (for blocking):** Mass stops transmission through walls.
3. **High absorption coefficient** over a wide range of frequencies.
4. **Fire resistant and non-combustible.**
5. **Resistant to moisture, termites and fungus.**
6. **Durable, easy to fix and clean, and low in cost.**
7. **Good appearance** so that it can be used on exposed surfaces.

#### Examples

| Type | Examples |
|---|---|
| Sound absorbers | Acoustic tiles, perforated gypsum boards, mineral and glass wool, fibre boards, cork, foam, felt |
| Sound barriers | Heavy brick or concrete walls, double walls with an air gap, lead sheet, dense boards |
| Vibration/impact isolators | Rubber pads, cork underlay, carpets, floating floors |

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Why should absorbing materials be porous and light?
   A. Sound enters pores and is changed to heat
   B. To reflect sound
   C. To look good
   D. To burn
   Answer: A. Sound energy entering the pores is converted to heat. (Key point: Absorption)

2. Which property stops transmission through walls?
   A. Lightness
   B. Heavy and dense mass
   C. Porosity
   D. Transparency
   Answer: B. Mass blocks transmission. (Key point: Blocking)

3. Which is a sound barrier?
   A. Acoustic tile
   B. Cork
   C. Heavy concrete wall or lead sheet
   D. Felt
   Answer: C. Heavy walls, double walls with air gap and lead sheet are barriers; tiles, wool, cork absorb. (Key point: Examples)

## Related in Civil Engineering Materials

- [Insulating materials in brief](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Ainsulating-materials) — Civil Engineering Materials, chapter 10, asked 3×

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