Published: 2026-10-16 · Category: Selection guide
Paper is usually specified by grammage, but stiffness is what decides whether an element keeps its shape through assembly and service. The two are related, and they are not the same thing.
How they relate
Basis weight is fibre mass per unit area; stiffness is resistance to bending. Raising weight normally raises stiffness, but not linearly - fibre blend, refining degree, calendering and resin impregnation all move stiffness at a given weight. In other words, the same grammage can be supplied at different stiffness.
When higher stiffness is needed
- Tall pleats: the taller the pleat, the more bending and spring-back the paper sees; insufficient stiffness gives collapse or uneven spacing;
- Compressed assembly: end caps pressed on or potted in adhesive require the paper to spring back and hold shape;
- Pressure pulses: cold starts and flow transients load the element; weak paper deforms;
- No centre tube: without internal support the paper carries more of the shape-keeping duty.
Low weight with high stiffness is achievable
Solving stiffness purely by adding grammage costs pressure drop, material and pleat envelope. In production it is more usual to keep a sensible weight and raise stiffness through the resin system and calendering, so the element holds shape without dragging the pressure drop up. How far that can go depends on the sheet and the impregnation conditions, so it is settled by sampling.
Four questions worth asking
- What are the pleat height, pleat count and element face dimensions?
- How is it assembled - pressed end caps, adhesive, centre tube support?
- Will the element see significant pressure pulses, for example on cold start?
- Are there temperature, oil resistance or flame-retardant requirements?