Coroplast yard signs are the workhorse of election campaigns, real-estate marketing, event signage and contractor advertising - and one of the highest-volume products a sign distributor buys. They are also deceptively simple: a corrugated plastic sheet is not a commodity once you look at thickness, gram weight, flute direction and print method, all of which change how the sign performs in a front lawn and what it costs per unit. This buyer's guide explains the specifications that matter when sourcing coroplast signs in bulk, so you can compare quotes on a like-for-like basis and order boards that stay flat, readable and upright through the whole campaign.
What Coroplast Actually Is
Coroplast - also sold as corflute, correx, corrugated plastic or twin-wall polypropylene - is an extruded polypropylene (PP) sheet with two flat skins separated by vertical ribs called flutes. The hollow structure gives it a rare combination of properties: it is lightweight yet rigid, fully waterproof, tear-resistant, chemically inert, reusable and 100 percent recyclable.
Standard sheet size is 4 x 8 feet (1220 x 2440 mm), from which signs are cut to size - 18 x 24 inches being the classic yard sign. Because polypropylene naturally repels ink, sign-grade sheets receive a corona treatment that raises surface energy (typically to 46 dynes/cm) so inks and UV prints bond reliably. When comparing suppliers, confirm the sheet is corona-treated graphic grade, not packaging grade. Boards can also be specified with UV stabilizers for longer outdoor exposure, which is worth the small premium on season-long programs.
Thickness and Weight: The Two Numbers That Define the Board
Coroplast is specified by thickness (2 to 12 mm) and by gram weight (gsm - grams per square meter). Thickness sets stiffness; gsm tells you how much plastic is actually in the sheet, and two 4 mm boards of different gsm are not the same product. Higher gsm means thicker skins and ribs, better rigidity and better resistance to bending in wind.
| Thickness | Typical weight range (gsm) | Best suited for |
|---|---|---|
| 2 mm | 250-450 | Disposable indoor signs, short-term displays |
| 3 mm | 300-600 | Indoor retail signs, light promotional boards |
| 4 mm | 600-900 | Standard yard signs, real-estate and campaign signs |
| 5 mm | 800-1200 | Sturdier outdoor signs, reusable displays |
| 6 mm | 900-1600 | Long-term outdoor signage, larger panels |
| 8 mm | 1400-2000 | Heavy-duty outdoor boards, site signage |
| 10 mm | 2600-3000 | Maximum rigidity; construction and directional signs |
For most yard sign programs, 4 mm at 650-750 gsm is the value standard; move to 5 mm or 6 mm when signs are larger than 24 x 36 inches or must survive a full season outdoors. A suspiciously cheap 4 mm quote is often a 550 gsm board - always ask for the gsm.
Flute Direction and Why It Matters
The flutes are the hollow channels running through the sheet, and their direction is not a cosmetic detail - it determines how the sign mounts. The ubiquitous wire H-stake (also called a step stake) works by sliding its two prongs up into the flutes. That only works when the flutes run vertically relative to the printed face of the sign.
Ordering mistakes here are expensive: a pallet of signs with horizontal flutes cannot take H-stakes and must be grommeted and tied instead. Always state flute direction on your purchase order - vertical flutes for stake-mounted yard signs, horizontal only if the sign will be screwed, taped or framed. Flute direction also affects rigidity: a wide sign with vertical flutes bows less along its top edge than one with horizontal flutes.
Print Options: Screen, UV and Digital
Three processes cover coroplast, and the right one depends on artwork and quantity:
- Screen printing is the volume champion. One to three spot colors print fast and cheap per unit, with thick, opaque ink that survives years outdoors. Campaign signs of 500 pieces or more with simple bold artwork are classic screen work.
- UV flatbed printing jets ink directly onto the board and cures it instantly. It handles full-color photographs, gradients and white ink, suits runs from a handful to a few hundred boards, and needs no screens - ideal when every sign in a batch carries different artwork, such as real-estate agent panels.
- Digital printing on adhesive vinyl applies a printed vinyl decal to the coroplast. It makes sense for short runs needing laminated, scuff-resistant graphics, though direct UV printing has largely taken over this role.
Whichever process you choose, print both sides unless the sign mounts against a wall - double-sided printing costs little extra on coroplast and doubles the exposure.
Sizes, Finishing and Hardware
Common wholesale sizes run from 12 x 18 inches up to 48 x 96 inches, with 18 x 24 and 24 x 36 inches dominating yard sign programs. Custom shapes are die-cut cheaply at volume. Finishing options to specify include corner rounding, grommets for fence mounting, drilled holes, and edge sealing for hygiene-sensitive or long-term reuse.
Hardware is usually sourced with the signs: H-stakes in standard and heavy-duty gauges, tall step stakes for roadside visibility, and A-frames that grip two boards back to back. Ordering signs and stakes from one supplier guarantees the stake prongs match your flute spacing and sheet thickness - mismatched stakes that splay the flutes are a common cause of failed installations in the field.
One more export note: coroplast is light but bulky, so freight cost is driven by volume rather than weight. Cutting boards to final size before shipping instead of sending full sheets, flat-packing the stakes, and nesting components efficiently all reduce cubic volume. Discuss packing format with your supplier at quote stage - on large programs the freight saving can exceed any saving negotiated on print price.
Bulk Buying Checklist
Put these seven items on every coroplast RFQ and the quotes you receive become directly comparable:
- Thickness in mm and weight in gsm (for example, 4 mm / 700 gsm).
- Sheet grade: corona-treated graphic grade for printing.
- Finished size and flute direction (vertical for H-stakes).
- Print process, number of colors and number of sides.
- Finishing: corners, grommets, die-cut shape.
- Hardware: stake type and quantity.
- Quantity per design and total order volume.
Common Mistakes When Ordering Yard Signs
Five recurring errors cause most coroplast complaints. First, buying on thickness alone and ignoring gsm, so a flimsy low-weight board arrives where a rigid one was expected. Second, forgetting to specify flute direction, leaving H-stakes useless on delivery day. Third, ordering single-sided prints for roadside locations where traffic approaches from both directions. Fourth, cramming too much text onto the design - a yard sign is read at 30 mph, so seven words and one clear message outperform a paragraph every time. Fifth, skipping the sample: color, board weight and stake fit should all be approved on a physical sample before a 5,000-piece run ships across the ocean. None of these mistakes costs much to prevent; all of them are expensive to fix after production.
How Sainthouse Can Help
Sainthouse Technology has manufactured printed coroplast yard signs in Qingdao, China since 1998, supplying distributors and sign shops worldwide. We screen print and UV print coroplast from 4 mm to 10 mm in cut sizes and custom shapes, with stakes and finishing supplied to match. Minimum orders start from 500 pieces, and we produce a printed sample for approval before every production run. Send your size, thickness, artwork and quantity for a firm quotation.
References
- Huiyuan Plastic - Polypropylene Corrugated Plastic Sheet: Thickness Options and Applications: https://www.corrugatedppsheets.com/?p=25469
- Ecore Pack - Thick Corrugated Plastic Sheets Technical Data (thickness vs gsm): https://m.made-in-china.com/product/Thick-Corrugated-Plastic-Sheets-for-Outdoor-Waterproof-Coroplast-and-Lightweight-Blank-Yard-Signs-1988201252.html
- Huiyuan Plastic - 4 mm Corflute Sheets Specifications: https://www.corrugatedppsheets.com/product/4mm-corflute-sheets