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Foam glass aggregate vs pumice for lightweight fill

Caltrans lists natural volcanic lightweight material, the group pumice belongs to, at 800 to 1,200 kg/m³ (50 to 75 lb/ft³).[1] FHWA lists foam glass aggregate at 160 to 400 kg/m³ (10 to 25 lb/ft³).[2] On Vancouver's Killarney Park field, Enviro-Rock was accepted as the approved equal to the specified pumice.[3]

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Enviro-Rock at a glance

Loose dry bulk density
200 kg/m³
Angle of friction
39° at 65 kPa
Thermal resistance
R-2.4 per inch, dry
Up to, per B-train load
140 m³

From the Enviro-Rock specification table and delivery trailer sheet. Sources on the product page.

Side by side

Foam glass aggregate vs pumice

FactorFoam glass aggregatePumice
MaterialManufactured from recycled glass that is milled to a powder, mixed with a foaming agent and heated in a kiln.[2] State specifications require at least 95 to 98% recycled glass.[4][5]Natural volcanic material. Caltrans lists it as a common lightweight fill.[1]
Unit weight160 to 400 kg/m³ (10 to 25 lb/ft³) across the material class.[2] Enviro-Rock: 200 kg/m³ (12.5 lb/ft³) loose, 240 kg/m³ (15.0 lb/ft³) at 20% compaction.[6]800 to 1,200 kg/m³ (50 to 75 lb/ft³) for natural volcanic material.[1] On one Caltrans embankment, TxDOT reports pumice aggregate estimated at 1,120 kg/m³ (70 lb/ft³) in place.[7]
Weight compared with ordinary fillMineral soils and aggregates weigh 1,520 to 2,400 kg/m³ (95 to 150 lb/ft³), against 160 to 400 kg/m³ for foam glass aggregate.[2]About half the weight of ordinary mineral soils and aggregates, which FHWA lists at 1,520 to 2,400 kg/m³ (95 to 150 lb/ft³).[2][1]
Agency recognitionNew York and Indiana publish specifications for foam glass aggregate fill, and Maine DOT has used a project special provision.[8][5][4] Enviro-Rock is an accepted product in the Lightweight Fill category of the BC Ministry of Transportation and Transit Recognized Products List.[9]Caltrans lists natural volcanic material as a common lightweight fill. Its January 2026 ground modification manual does not list foam glass aggregate.[1]
Acceptance testingPublished specifications set limits on gradation, density, friction angle and compressive strength, and New York checks density on every truckload.[4][8] Enviro-Rock test reports are available on request.[10]Ask the supplier for gradation, unit weight, strength and absorption results for the material being supplied.
Track record in VancouverAbout 11,000 m³ of Enviro-Rock went in as the lightweight fill beneath the Killarney Park soccer field.[3]Pumice was the lightweight fill originally specified for that field.[3]

Where foam glass aggregate fits

When foam glass aggregate is the better choice

Foam glass aggregate wins where the job of the fill is to take load off soft ground or a structure. Caltrans's range for natural volcanic fill starts at 800 kg/m³, twice the top of the FHWA range for foam glass aggregate.[1][2]

It also comes with published acceptance criteria. New York and Indiana specifications and a Maine DOT project provision set limits on its density and gradation, and Enviro-Rock is an accepted lightweight fill on the BC Recognized Products List.[4][8][5][9]

Killarney Park is the local precedent: about 11,000 m³ of Enviro-Rock went in beneath the field in place of the specified pumice.[3]

Where pumice fits

When pumice may be the better choice

  • The project follows Caltrans guidance, which lists natural volcanic fill and does not list foam glass aggregate.[1]
  • A pumice source is close to the site and the design can accept a fill of 800 to 1,200 kg/m³.[1] Shipping distance is a main driver of foam glass aggregate cost.[11]
  • The specification already names pumice and the schedule leaves no time for an approved-equal review.

Questions

Common questions

Is foam glass aggregate lighter than pumice?

Yes, by published ranges. FHWA lists foam glass aggregate at 160 to 400 kg/m³ (10 to 25 lb/ft³), and Caltrans lists natural volcanic material, which includes pumice, at 800 to 1,200 kg/m³ (50 to 75 lb/ft³).[2][1]

Can Enviro-Rock be submitted as an approved equal to pumice?

It has been. At Killarney Park in Vancouver, Enviro-Rock was accepted as the approved equal in place of the originally specified pumice.[3] Acceptance on any project rests with the project owner and the engineer of record.

Does foam glass aggregate float?

Yes. It is buoyant, so designs keep it above groundwater and flood levels or hold it down with cover material.[12] At Jim Lorimer Park in Burnaby, the Enviro-Rock design anchored the fill against uplift because the site floods seasonally.[13]

Does foam glass aggregate absorb water?

Enviro-Rock absorbs 7.2% uncompacted, and its closed internal cells limit water entering each particle.[6][14] For the material class, 28-day absorption is commonly 30 to 60% by weight, which is small by volume because the aggregate is so light.[15][12]

What drives the delivered cost of foam glass aggregate?

Shipping distance is a main driver.[11] Lightweight fills usually fill a truck's volume before its weight limit, so large trailers matter: an Enviro-Rock B-train carries up to 140 m³ (about 183 yd³).[7][16]

Sources

  1. [1] Ground Modification, Geotechnical Manual, Caltrans, 2026
  2. [2] Alternative Backfills for Highway Applications: State of the Practice (FHWA-HRT-23-110), Federal Highway Administration, 2024
  3. [3] Case study: Killarney Park soccer field, Vancouver, Enviro-Corp Recycling
  4. [4] Special Provision Section 203, Ultra-Lightweight Foamed Glass Aggregate, Maine DOT, 2025
  5. [5] 904-M-076 Lightweight Aggregate, Indiana DOT, 2025
  6. [6] Enviro-Rock civil infrastructure brochure (metric), specification table, Enviro-Corp Recycling
  7. [7] Guidelines for Using Lightweight Fills in Transportation Infrastructure Applications, Texas DOT and University of Texas at Austin, 2025
  8. [8] Item 203.03200017, Lightweight Foamed Glass Aggregate Fill, New York State DOT, 2023
  9. [9] Recognized Products List, Lightweight Fill Material (October 1, 2026), BC Ministry of Transportation and Transit
  10. [10] Enviro-Rock technical data, Enviro-Corp Recycling
  11. [11] Applications for Foamed Glass Lightweight Aggregate, research summary, Washington State Transportation Center (TRAC), 2025
  12. [12] Applications for Foamed Glass Lightweight Aggregate, final report, Illinois Tollway Research Program, Washington State University et al., 2025
  13. [13] Case study: Jim Lorimer Park playground, Burnaby, Enviro-Corp Recycling
  14. [14] Enviro-Rock benefits: closed-cell structure, Enviro-Corp Recycling
  15. [15] 904-M-076 Lightweight Aggregate, Indiana DOT, 2025
  16. [16] Enviro-Rock delivery trailer overview, Enviro-Corp Recycling

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