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When you request a quote for a flexible water tank from a Chinese manufacturer, the specification sheet will list a fabric weight in gsm and a nominal thickness in millimetres. These two numbers matter more than almost any other specification — they determine how long the tank will last, how much it weighs empty, and what internal pressure it can sustain. Here is what the numbers mean in practice.
What gsm Means
gsm stands for grams per square metre — the weight of one square metre of the coated fabric. A higher gsm means more PVC coating material, which generally translates to greater puncture resistance, better UV stability, and longer working life. It also means a heavier, thicker fabric that is slightly less pliable when folding and rolling for transport.
The gsm figure includes both the base fabric (usually a polyester woven scrim) and the PVC coating applied to both sides. A well-specified sheet will also state the coating thickness separately in millimetres and the tensile strength in both warp and weft directions.
650 gsm — Light Duty
650 gsm fabric is the lightest grade commonly used in flexible water tanks. It is pliable, easy to fold, and lightweight to handle. It is appropriate for short-term temporary storage over weeks to a few months, low-pressure ground-level installations, agricultural applications where the tank is filled and emptied frequently, and emergency reserve tanks that are rarely filled to capacity.
The trade-off is durability. At 650 gsm, abrasion resistance is lower, UV exposure accelerates degradation faster, and seam stress at full capacity leaves less margin. This grade is not recommended for permanent or semi-permanent outdoor installation.
850 to 950 gsm — Standard B2B Export Grade
This is the most widely specified range for B2B export flexible water tanks. At 850 to 950 gsm with approximately 0.9 mm nominal coating thickness, the fabric offers a practical balance between weight, flexibility, and working life. This specification is appropriate for construction site water storage with repeated fill and empty cycles, agricultural and irrigation reserve tanks in seasonal outdoor use, cube and pillow tanks in the 1,000L to 20,000L range, and export projects where handling, transport, and moderate outdoor exposure are expected.
A well-executed HF-welded seam on 850 gsm fabric should have greater tensile strength than the fabric panel itself — the panel will fail before a quality seam does.
1,000 gsm and Above — Industrial and Heavy Duty
Tanks above 1,000 gsm are used for demanding industrial applications or very large capacities where the hydrostatic pressure on lower panels requires additional fabric strength. This range is common for large pillow tanks above 20,000L, long-term outdoor installation in high-UV environments such as mining and remote sites, applications involving chemical compatibility requirements, and situations where tank replacement would be expensive or logistically difficult.
The higher gsm adds meaningful weight to the tank and reduces flexibility when folding — this should be factored into deployment planning, especially if the tank needs to be repositioned regularly on site.
What to Ask Your Supplier
When comparing suppliers, ask for the full fabric specification: gsm weight, coating thickness in mm, base fabric denier or thread count, tensile strength in both warp and weft directions, and tear resistance. A reputable factory will have a certified test report for their fabric from an accredited laboratory. If a supplier cannot provide this document, the stated specification is unverified.
Be cautious of very low prices on tanks specified at 850 gsm or above — this often indicates the actual fabric delivered is lighter than stated, a difference that is difficult to verify without physical testing.
ZolinWorks Fabric Specification
ZolinWorks produces standard tanks in 850 to 950 gsm HF-welded PVC-coated fabric with 0.9 mm nominal coating thickness. Industrial and large-capacity tanks — typically above 18,000L — use reinforced fabric in the 900 to 1,100 gsm range. Custom fabric specifications are available for project-specific requirements.
Send your capacity, application, and environment details and we will confirm the appropriate fabric grade for your order.
Further reading: Browse the PVC water tank collection, compare seam construction in our HF-welded vs adhesive-bonded guide, or read the buyer checklist for sourcing from China.