Artificial grass underlay, also called a shock pad or performance pad, is a layer of foam or bonded rubber laid between the base and the turf. It softens the surface, cushions falls, hides small imperfections in a hard substrate and in some designs channels water sideways to a drain. It is not part of every installation, and adding one changes how the base and edges are built. The installers we work with on artificial turf with shock pad installation treat the pad as a structural layer, not an afterthought, because a pad laid on a poor base or with the wrong drainage path causes problems a bare turf install would not.
What artificial grass underlay does
Synthetic turf itself is thin. The pile is held in a backing a few millimeters thick, and most of the cushion you feel on a well-built lawn comes from the infill and the base below. A pad adds a controlled, consistent layer of give. The three reasons to add one are comfort, fall protection and substrate correction.
Comfort is self-explanatory: a 10 to 20 millimeter pad makes turf over concrete feel closer to a lawn than a carpet. Fall protection is a measurable property. Playground surfacing in the US is tested to ASTM F1292, which rates the fall height a surface can absorb. Turf alone does not meet meaningful fall heights; turf over a rated shock pad can. Substrate correction covers cases where the surface under the turf is hard and slightly uneven, such as old concrete with hairline cracks or a composite deck with board gaps, where a pad bridges the imperfections so they do not telegraph through the pile.
Types of pad and where each fits
Pads differ in material, thickness, density and how they handle water. Choosing the best artificial grass underlay for a project means matching those traits to the use.
| Pad type | Typical thickness | Drainage | Best for |
|---|---|---|---|
| Closed-cell polyethylene foam | 5 to 12 mm | Perforated holes; water passes vertically | Patios, balconies, comfort over concrete |
| Cross-linked PE foam with drainage channels | 10 to 25 mm | Grooved underside moves water sideways to an edge drain | Rooftops, decks, slabs with a single fall direction |
| Bonded rubber (recycled SBR) shock pad | 20 to 50 mm | Porous; water passes through | Playgrounds, fall-height ratings, school fields |
| Expanded polypropylene (EPP) panels | 15 to 30 mm | Interlocking with drainage holes | Sports fields, pet runs, high-traffic lawns |
| Poured-in-place rubber | Variable | Porous | Commercial play areas, odd shapes |
Do you need underlay for artificial grass on concrete?
Usually yes, for two reasons that have nothing to do with comfort. First, concrete does not drain. Water that passes through the turf backing has nowhere to go except sideways across the slab, and if the slab is flat or has a low spot, it pools under the turf, grows algae and lifts the glue. A pad with drainage channels on the underside gives that water a path to the slab edge or a drain. Second, concrete is unforgiving. Every crack, trowel ridge and expansion joint shows through a thin pile within weeks as the infill settles. A pad hides them.
Artificial grass underlay for concrete should be laid on a clean, dry slab, with the drainage channels running in the direction the slab falls. The pad is bonded at the perimeter and along joints so it cannot creep, and the turf is then glued to the pad or to a perimeter strip rather than nailed, because there is nothing to nail into. If the slab has no fall at all, the installer either cuts a drain or builds a thin screed to create one before anything else goes down. Learn more about how base drainage is designed in our page on artificial turf drainage.
Pro tip: Pour a bucket of water on the slab before the install and watch where it goes. If it sits, the pad alone will not fix it. Drainage has to be solved first, then cushioned.
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Artificial grass underlay drainage
On a conventional aggregate base, water passes through the turf backing, through the pad and into the compacted stone where it percolates away. A pad in this setting must be perforated or porous so it does not act as a sheet of plastic over the stone. Perforation spacing of roughly 2 to 4 inches is common, and the holes should line up with the drainage holes punched in the turf backing as much as possible, though in practice the infill and pad surface spread water enough that exact alignment is not critical.
When a pad is worth it and when to skip it
Skip the pad
- Landscape lawn on a 3 to 4 inch compacted aggregate base
- Low fall-height risk, no play equipment
- Pile height 1.5 inches or more with full infill depth
- Soil that drains well and a base built to drain
Add a pad
- Turf over concrete, pavers, decking or a rooftop
- Under swings, climbing frames or trampolines
- Pet runs on a hard base where flushing matters
- Short-pile sports or gym turf where joints take impact
- Any surface where a flat, cushioned feel is the goal
Pads also change fastening: turf is glued to the pad at seams and perimeter rather than nailed, so repairs differ from a nailed lawn; see our guide to artificial turf repair.
A pad will not rescue a bad base. It adds comfort and cushioning on top of a base that is already stable and drains. If a quote proposes a pad as the fix for soft or uneven ground, that is a reason to ask more questions about excavation and compaction.
Getting the pad installed correctly
If your project involves concrete, a rooftop, a play area or a pet run, make sure the installer has done pad work before and can describe how they handle drainage and fastening. The artificial turf installation crews we match homeowners with are asked those questions up front.
Artificial grass underlay FAQ
Do you need underlay for artificial grass on concrete?
In almost every case, yes. A pad hides slab imperfections and, more importantly, gives water a path to drain across a surface that cannot absorb it.
What is the best artificial grass underlay for a play area?
A bonded rubber or EPP shock pad tested to ASTM F1292 for the fall height of the equipment. Thin foam comfort pads are not rated for fall protection.
Does underlay affect artificial grass drainage?
Only if the wrong pad is used. Perforated or porous pads let water pass vertically to the base; channeled pads move it sideways on slabs. An unperforated closed-cell pad will trap water.
The complete turf installation guide
What a quality install looks like, the eight installation steps, spec sheets, and how to choose an installer.