RPP Geomembrane Specifications
Reinforced polypropylene (RPP) is a scrim-reinforced geomembrane: flexible polypropylene plies laminated over a woven polyester scrim that carries the tensile load. Its flexibility and large factory-welded panel sizes make it a default choice for floating covers, baffle curtains, and prefabricated pond liners in long-term exposed service. Because RPP is a fabric-reinforced membrane, its properties are defined by the ASTM D751 test family and the GRI-GM18 specification rather than the sheet-plastic methods used for HDPE.
Material properties and test methods
| Property | Test method | Notes |
|---|---|---|
| Construction | Manufacturer data sheet | Two or more polypropylene plies laminated over a woven polyester scrim; the plies form the barrier and weathering surfaces, the scrim carries load |
| Thickness | ASTM D5199 / D751 | 36 mil and 45 mil are the common reinforced grades; nominal thickness includes both plies and the encapsulated scrim |
| Grab tensile strength | ASTM D751 (Grab Method) | Reinforced membranes are tested with fabric methods; minimum values are set by GRI-GM18 and the manufacturer's published data sheet |
| Tongue tear strength | ASTM D751 | The polyester scrim arrests tear propagation, a key advantage over unreinforced sheet in exposed, wind-loaded service |
| Puncture resistance | ASTM D4833 / FTM 101C | Scrim reinforcement distributes point loads across the weave |
| Hydrostatic resistance | ASTM D751 Method A | Verifies the laminate resists water pressure without ply delamination or leakage |
| Low temperature bend | ASTM D2136 | RPP remains flexible in cold service and resists cold-crack, which matters for exposed covers that flex daily |
| Dimensional stability | ASTM D1204 | Low shrinkage after heat exposure keeps prefabricated panel geometry true |
| Ply adhesion | ASTM D413 / D751 | Confirms the coating plies stay bonded to the scrim over service life |
| Grade | Typical use | Selection notes |
|---|---|---|
| 36 mil RPP (reinforced) | Floating covers, baffle curtains, exposed pond and reservoir liners, prefabricated drop-in liners | The workhorse grade; balances weight, foldability, and strength for factory panelization |
| 45 mil RPP (reinforced) | Larger exposed covers and liners where specifications call for added thickness and service life | Heavier plies over the same scrim concept; specified where owners want extra weathering allowance |
| Unreinforced polypropylene (fPP) | Detail work, boots, and fittings where high elongation matters more than tensile strength | Welds compatibly with reinforced sheet, which simplifies penetration and sump details |
What scrim-reinforced polypropylene is
RPP is a composite geomembrane. A woven polyester scrim, typically a 1000-denier weave, is laminated between plies of flexible polypropylene. The polypropylene provides the waterproof barrier, chemical resistance, and UV-stabilized weathering surface. The scrim does the structural work: it carries tensile load, stops tears from propagating, and holds panel dimensions stable under thermal cycling and wind uplift.
This division of labor is what separates RPP from unreinforced sheet materials. An unreinforced membrane must rely on sheet thickness alone for strength, so it gets stiffer as it gets stronger. RPP gets its strength from the scrim, so the sheet can stay thin, light, and foldable while still meeting demanding grab tensile and tongue tear requirements.
Standard thicknesses and weights
The two standard reinforced grades are 36 mil RPP and 45 mil RPP, with the mil count describing total nominal thickness of the plies plus the encapsulated scrim. 36 mil is the most commonly specified grade for floating covers, baffle curtains, and prefabricated pond liners. 45 mil is selected when a specification calls for additional weathering allowance or a longer stated service life in exposed conditions.
Because RPP is roughly half the weight of comparably specified thicker sheet goods, a factory-fabricated panel covering tens of thousands of square feet can still be folded onto a pallet, shipped conventionally, and deployed by a small crew. Exact roll weights, panel size limits, and warranty terms come from the manufacturer's published data sheet and should be confirmed during submittal review.
How RPP is tested: the D751 fabric family and GRI-GM18
Reinforced membranes are tested as coated fabrics, not as homogeneous plastic sheet. ASTM D751 is the governing family: grab tensile strength, tongue tear strength, hydrostatic resistance, and ply adhesion all run under D751 procedures. Thickness is measured under ASTM D5199 or D751, puncture under ASTM D4833, low temperature bend under ASTM D2136, and dimensional stability under ASTM D1204.
GRI-GM18 is the Geosynthetic Institute specification covering flexible polypropylene geomembranes, both reinforced and unreinforced. It sets minimum property values per grade and defines the required test methods and frequencies, giving specifiers a neutral benchmark to write around instead of a single manufacturer's brochure. A well-written RPP section cites GM18 and then lists the project-specific values the submittal must meet.
This is a different framework from HDPE, which is specified under GRI-GM13 with sheet methods such as ASTM D6693 tensile and D5820 seam testing. Comparing an RPP grab tensile number to an HDPE yield strength number is comparing two different tests; the material comparison has to happen at the application level.
UV, chemical, and exposure performance
RPP is formulated for long-term exposed service. The polypropylene plies are compounded with UV stabilizers and carbon black or pigments, and manufacturers publish accelerated weathering data under xenon-arc methods such as ASTM G155 to support exposed-service warranties. Floating covers and baffle curtains spend their entire lives in sun, wind, and water, which is exactly the duty RPP was developed for.
Chemically, polypropylene handles the water, wastewater, and dilute chemical environments typical of ponds, reservoirs, and treatment basins. Like most polyolefins it is not suited to sustained hydrocarbon or strong oxidizer contact, so fuel-related containment usually points to other materials. Chemical compatibility should always be verified against the manufacturer's resistance chart for the actual stored liquid, concentration, and temperature.
Why RPP dominates prefabrication and floating covers
Prefabrication is where RPP earns its place. Because the sheet is flexible and light, large panels can be thermally welded in the shop under controlled conditions, tested, folded, and shipped to site as a single unit. That moves most of the seaming off the jobsite, shortens field schedules, and reduces the number of field welds that need destructive testing. Stiffer sheet materials cannot be folded this way and must be seamed panel by panel in the field.
The same flexibility is what floating covers and baffle curtains demand mechanically. A floating cover flexes with every change in water level and every wind event; a baffle curtain hangs in the water column and moves with flow. RPP tolerates that continuous flexing without stress cracking, and its D2136 cold-bend performance means it keeps flexing through winter service. Field seaming and repairs use hot-air or hot-wedge fusion welding, and seams can be verified with air-channel or vacuum testing per the project specification.
Where RPP fits and when to look elsewhere
Specify RPP when the membrane will live exposed, needs to be prefabricated into large panels, or must flex in service: floating covers, baffle curtains, drop-in pond liners, and exposed reservoir linings are the core applications. Specify a different material when the duty is aggressive chemical containment, very high temperature, or a large open earthwork liner where field-welded HDPE under GRI-GM13 is the established default. Our comparison of HDPE and RPP walks through that decision in detail, and our fabrication team can review a project specification and confirm which material and grade the submittal should carry.
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