How to Choose

Mid-century modern sofa - soft back cushions + firm seat cushions - learn how to choose the right firmness

As a rule, back cushions are soft, and seat cushions are firm

Natural latex foam for upholstery: Learn the four factors that affect your choice of upholstery foam for sofa cushions or ‘tight’ upholstery (attached directly to the underlying frame or seat foundation). First, let’s look at the terms:

Firmness & Density – defined

It’s important to make the distinction between firmness & density, which are the two verifiable, scientific measurements used to rate the feel and quality of ALL foams, including natural latex.

FIRMNESS = Comfort (measured as pressure to compress a given thickness by a given amount)

  1. interprets the feel of foam and how it yields to weight and pressure
  2. is designated by the term ‘Indentation Load Deflection’, or ILD (also known as ‘Indentation Force Deflection’, or IFD), determined by mechanical performance testing in which a standardized foam sample is used to measure the force in pounds that it takes a 50 square inch circular indenter to compress the material by 25 percent of its thickness
  3. a very firm foam material will require greater force to reach the same compression as a softer material, and thus will have a higher ILD rating
  4. Note: ILD is only accurate when comparing the same type of latex from the same latex manufacturer. For our purposes, we are talking about 100% Natural Dunlop Latex.
Machine measuring latex firmness

Firmness testing machine

DENSITY = Weight (measured as weight of a given volume of material)

  1. Density is a measurement of the mass per unit of volume – for latex expressed as kilograms/cubic meter (converted to lbs/cubic foot to remain consistent with units of measurement familiar to the U.S. upholstery industry)
  2. Density in natural dunlop latex usually varies from around 60 kg/m3 to about 95 kg/m3 (4.4 lb/ft3 – 5.9 lb/ft3)
  3. If a latex foam has a density rating of 95D, that means a 1 meter x 1 meter x 1 meter block weighs 95 kilograms (or a 1 foot x 1 foot x 1 foot block weighs 5.9 pounds).
antique carved oak daybed with natural and organic upholstery cushions

Antique carved oak daybed with natural and organic upholstery 

Firmness, ILD ratings & Densities for 100% Natural Dunlop Latex Foam:

  • soft (16-18 ILD) – Density: 65 kg/cubic meter (4.1 lbs/cubic foot) – N25
  • medium (23-27 ILD) – Density: 75 kg/cubic meter (4.7 lbs/cubic foot) – N28
  • firm (28-33 ILD) – Density: 80-85 kg/cubic meter (5.0 lbs/cubic foot) – N31
  • x-firm (34-48 ILD) – Density: 90-95 kg/cubic meter (5.6 lbs/cubic foot) – N36
  • hard (39-43 ILD) – Density: 95+ kg/cubic meter (5.9 lbs/cubic foot) – N45

Firmness is Subjective

If you’re doing your own upholstery project, such as replacing a sofa cushion, re-covering your dining chairs with new foam, or building a new window seat cushion, keep in mind that different foam firmnesses are recommended for different purposes.

The comfort of any cushion depends on these FOUR VARIABLES:

  1. Your preference (do you like to sink into your furniture, or feel more supported?)
  2. Your weight (more weight requires higher density / firmness)
  3. The designated use (seat or back cushion on a sofa, window seat, etc)
  4. Thickness of the cushion (a thicker foam with the same ILD rating feels firmer)

Grandfather and granddaughter laughing on sofa

General recommendations for Latex Foam firmness

For a 5-6” thick seat cushionthe most popular firmness is 31-35 ILD (firm); 26-30 ILD (medium) feels soft – for those who like to sink into the sofa; for those who prefer a firmer seat cushion with plenty of support, 36-42 ILD (extra-firm) is a good choice for this thickness.

The thinner the foam, the less support it gives per unit of body weight, so the higher the firmness (ILD) you need. For example, if you’re buying 1-2 inch thick foam for a dining chair seat, it won’t take much weight to ‘bottom out’ with this thin application, so you’ll want to order the firmest foam to achieve the greatest comfort.

A sofa or chair back cushion should be softer because ‘leaning on’ exerts less pressure than ‘sitting on’. For a 4” thick back cushion, the most popular firmness is 17-25 ILD (soft); choose 26-30 ILD (medium) for thinner back cushions or for a firmer feel.

Learn more about choosing the right foam for your upholstery project:

Download our FREE Guide to Natural Latex Foam Firmness & Density, to get natural latex upholstery foam firmness recommendations for different thickness applications, based on a specific body weight. Watch the video here: ‘How to Choose Natural Latex Foam Firmness for Your Upholstery Project’.

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