UnderBlock™ HD Rubber Floor Underlayment

FREE Standard Shipping Details


FREE Standard Shipping

Free shipping is valid on any order shipped to a single address in the mainland USA. Standard shipping is covered. Overnight or 2-day delivery will cost extra.

Our products are bulky and heavy. Free shipping is hard and expensive.

Read More About How We Do It

  • Buy 5 - 9 and get 15% off
  • Buy 10 - 14 and get 20% off
  • Buy 15 or above and get 25% off
In stock.
This product ships in 3-4 business days.

UnderBlock™ HD Rubber Flooring Underlayment

UnderBlock™ HD is the underlayment of choice for multi-family, hotels, and other large projects with high IIC requirements. Because most flooring (including many tiles) can be installed directly on top, save significant time during install while hitting 60+ IIC in many constructions. Contact us if you have questions about your specific assembly!



  • Subflooring / underlayment for reducing impact noise, airborne noise, and vibration
  • 100% recycled rubber
  • Most flooring can lay directly on top (including tile)
  • Best solution for maximum IIC and STC
  • Commonly specified and used in multi-family
  • Easy roll out installation
  • Proudly made in the USA




 Dimensions   4’ x 15’ (3/8”), 4’ x 13’ (1/2”) 
 Thickness   3/8" or 1/2"
 Weight    100 lbs (3/8) or 120 lbs (1/2") 
 Color    Black 
 R-value   2 per inch




 Spec Sheet 

 UnderBlock™ HD Product Sheet 

 Architect CSI Specs 

 UnderBlock™ HD CSI Spec 

 Install Guide 

 UnderBlock™ HD Install Guide 



Material Testing

For jobs with specific IIC requirements, contact us for to discuss your specific floor-ceiling assembly.



 Impact Insulation Class

 Roll Thickness   6" Concrete IIC 
 (LVT, No Ceiling) 
 8" Concrete IIC 
 (LVT, No Ceiling) 

 6" Concrete IIC 
 (Wood, No Ceiling) 

 8" Concrete IIC 
 (Wood, No Ceiling) 

3/8" 60 63 61 67
1/2" 58 64 65 68



Installation Instructions

  • Roll out UnderBlock™ HD to cover the subfloor. Adhesive is optional. UnderBlock™ HD is heavy and will not move around.
  • Use a metal straight edge to make any cuts with a sharp utility knife.
  • Leave a 1/8" gap between UnderBlock™ HD and any obstacles (walls, columns, posts, drains, pipes, etc). Fill this gap with acoustic sealant caulk.
  • For perimeter walls, you can run UnderBlock™ HD directly to or under the wall instead of leaving the 1/8" gap and sealing it.
  • Roll out the UnderBlock™ HD in rows, keeping the factory seams tight and flush. If the seams are flush, acoustic sealant is not needed. Joints and seams can be taped if desired.
  • Install your chosen flooring on top of UnderBlock™ HD rubber flooring underlayment. 



If you have any questions about your type of flooring for your project, call us and we can walk you through it!

  • Floating floors do not require additional adhesive. They just lay on top of UnderBlock™ HD.
  • Mechanically fastened floors (nail down) should have a subfloor glued to the top of UnderBlock™ HD. Use our recommended rubber adhesive when required.
  • Glue down floors should use whatever adhesive is recommended by the flooring manufacturer that is compatible with attaching to rubber.
  • When installing under carpet, UnderBlock™ HD should be cover the subfloor completely, leaving a 1/8" gap near obstacles to be filled with acoustical sealant. Tacking strips can be glued down to UnderBlock using our recommended rubber adhesive. Carpet padding is optional.



Common Product Uses

  • Multi-family condos, hotels, apartments, recording studios, conference rooms, commercial buildings, band rooms, houses of worship, theaters, schools, restaurants
  • UnderBlock HD delivers the best possible performance for a soundproof floor. It's the preferred choice for multi-family.
  • Meets building code for 6" or 8" concrete, even without a finished ceiling below.
  • Lay most flooring directly on top, including most tiles. 
  • Consider our standard sizes of Underblock™ Rubber Floor Underlayment