Replacing tired sofa cushions can be far more straightforward than replacing the whole sofa, provided the new foam is measured and chosen for the job rather than ordered from the old cushion by guesswork. The current All Foam range includes several upholstery foam sheets that can suit sofa seating, from balanced Medium Foam through firmer High-Firm and responsive Reflex grades. The right choice depends on the cushion cover, available depth, support underneath the seat, how often the sofa is used and the feel you want when you sit down.
This guide explains how to measure replacement sofa cushion foam, how to compare suitable grades and what to check before ordering. It is intended for removable seat cushions and similar domestic upholstery projects rather than giving one foam grade as a universal answer for every sofa.
When is it worth replacing sofa cushion foam?
Foam can gradually lose height and recovery after repeated compression. A cushion may start to look flatter at the front edge, take longer to return to shape or feel less supportive than neighbouring seats. In many cases the upholstery cover and sofa frame are still serviceable, so replacing the internal foam can refresh the seating without changing the entire piece of furniture.
Before ordering, check whether the problem is actually the foam. Remove the cushion and inspect the support beneath it. Webbing, springs, clips and platform boards can loosen or fail. If the base dips, a new foam cushion will follow that shape and may still feel unsatisfactory.
Also inspect the cover. Split seams, stretched fabric or badly distorted panels can change the finished fit. Foam cannot correct a cover that has become much larger or smaller than its intended shape. If the cover needs repair, have that work completed or accurately assessed before finalising the foam dimensions.
Measure the cushion cover, not only the tired foam
A common mistake is measuring an old cushion that has already compressed. Its current depth may no longer represent the space inside the cover.
If possible, remove the old filling and lay the empty cover naturally on a flat surface. Measure the internal or finished width, length and depth without pulling the fabric excessively. Take more than one measurement where the cover tapers or the seams are not perfectly square.
For a simple rectangular seat cushion, record:
- width from side seam to side seam;
- front-to-back length from the front seam to the rear seam;
- finished depth between the upper and lower panels;
- any taper from front to back;
- rounded corners, angled edges or other non-rectangular details.
The All Foam measuring guide explains the same principle for general cut-to-size foam: measure the space the new foam has to occupy rather than copying a worn piece blindly.
Do not automatically add a fixed amount to every measurement. Upholstery covers vary in stretch, construction and seam allowance. A small amount of controlled compression can help some covers look full, while too much oversizing can make the cushion difficult to insert, distort the seams or create an over-stuffed appearance. If the cover is valuable, unusual or heavily shaped, contact All Foam with the measurements before ordering.
Check whether the cushion is truly rectangular
Many sofa seats look rectangular until the cover is removed. The rear corners may be cut away around the arms, the front may be wider than the back, or one edge may have a gentle curve.
Measure each side independently. Do not assume the two long edges or two short edges are identical. For a tapered cushion, note both the front and rear widths. For a curved or irregular piece, a full-size template can be more reliable than a list of measurements.
Choose the foam by application and feel
Sofa seat cushions carry repeated body weight, so the starting point should be a foam intended for seating. The foam density and firmness guide explains why density and firmness are different properties and why neither should be considered in isolation.
Within the current All Foam upholstery range, the most relevant options for sofa seat cushions include the following.
Medium Foam for a balanced everyday feel
Medium Foam is a versatile upholstery grade with a balanced feel. It can suit deeper cushions and general seating where the customer does not want a particularly firm result.
It should not be chosen simply because the word medium sounds safe. A shallow cushion over a rigid base can feel and behave very differently from a deep cushion over webbing or springs. Consider the complete seat construction.
High-Firm Foam for a firmer sofa cushion
High-Firm Foam is intended for firmer-feel upholstery seating. It provides greater resistance to compression than the standard Medium grade and can suit customers who prefer a more supportive, less yielding seat.
Reflex Superior Medium for quicker recovery
Reflex Superior Medium follows the same broad application guidance as standard Medium Foam but offers a premium, resilient response with quicker recovery. It can suit customers who want a medium seating feel without the slower response associated with memory foam.
This makes it useful for sofa cushions where shape recovery and a responsive feel are priorities. It is not automatically firmer than every other option, so compare the stated application and feel rather than buying from the product name alone.
Reflex Superior Firm for a firmer resilient feel
Reflex Superior Firm is the firmer responsive alternative. It can suit premium upholstery projects where the customer wants more resistance to compression while retaining the quick recovery associated with Reflex foam.
Severe Very Firm for thinner seating applications
Severe Very Firm is reserved for applications that genuinely need a very firm grade, particularly thinner seating where there is less foam depth available to compress. It is not the default upgrade for an ordinary deep domestic sofa cushion. In a thick cushion, a very firm grade may feel unnecessarily hard if the customer expected conventional sofa comfort.
Cushion depth changes how the same foam feels
Thickness is not a firmness rating, but it affects the amount of material available to compress. A deep cushion can allow more movement through the foam than a thin pad made from the same grade.
That is why replacing a 100mm deep sofa cushion and replacing a 40mm dining chair pad should not be treated as the same job. The foam type, thickness, support beneath it and intended feel all work together.
If your sofa originally used a deep cushion and the cover still fits correctly, maintaining the designed finished depth is usually a better starting point than making the cushion thinner to save material. Changing the depth can alter seat height, knee position and the way the cover sits.
Consider the support underneath the cushion
Remove the seat cushion and press the support system with your hand. A solid timber platform gives a different feel from elastic webbing, metal springs or flexible slats.
If a webbed or sprung base has become loose, the cushion may sink further even after new foam is installed. Repairing the underlying support first gives the replacement cushion a fair chance to perform as intended.
For fixed-seat upholstery, check whether there are multiple foam layers, edge rolls or other components beneath the visible top layer. Replacing only one part of a more complicated upholstery build can change the geometry of the seat.
Should you copy the old foam grade?
Not always. The old cushion may not contain the grade you would choose today, and its original specification may be unknown.
Use the old foam as a clue rather than an absolute instruction. Note its original colour if it is still visible, whether it feels soft or firm in areas that have not been heavily used, and how thick it is around the least compressed edges. Then compare those observations with the current All Foam product descriptions.
Check fire information for the actual foam grade
Furniture foam should be selected with the relevant fire requirements in mind. All Foam product cards and technical data sheets provide the fire information for the individual grades.
Do not transfer a fire claim from one product to another simply because both are polyurethane foams. If the sofa is for a commercial, contract or other specification-led setting, confirm the complete requirement before ordering. The finished item, cover materials and upholstery construction may have obligations beyond the foam sheet itself.
Avoid these common sofa cushion replacement mistakes
The most frequent problems come from making assumptions before the cover and seat construction have been checked.
Measuring only the collapsed foam: the old filling may have permanently lost depth.
Choosing by colour: foam colour helps identify products but does not tell you whether a grade suits your application.
Assuming denser always means firmer: density and indentation resistance are different measurements.
Making every cushion oversized: controlled compression can help some covers, but a fixed oversize rule can distort others.
Ignoring the seat base: weak webbing or broken support can make new cushions feel as though they are failing.
Using a decorative padding grade for seating: light foams intended for headboards or general padding should not replace a specified seating grade.
A practical replacement sofa cushion checklist
Before ordering replacement sofa cushion foam, confirm:
1. The sofa frame, springs or webbing are still supportive. 2. The covers are in usable condition and have been measured independently. 3. Width, length and finished depth have been recorded in the same units. 4. Any taper, curved edge or cut-out has been identified. 5. The chosen foam is intended for seating. 6. The firmness suits the feel you actually want. 7. Cushion thickness has been considered alongside the foam grade. 8. Fire or contract requirements have been checked where relevant.
Replacing sofa cushion foam works best when it is treated as a small upholstery project rather than a simple block-for-block swap. Measure the cover carefully, check the support underneath and choose the grade by application and preferred feel. If you are unsure between Medium, High-Firm or a Reflex option, the All Foam team can help you compare the current foam sheet specifications before you order.