Swimwear Fabric Selection: Chlorine Resistance, UPF and Shape Retention
Swimwear is the most hostile application in the apparel range. Fabric is exposed to chlorine, salt, sunscreen, heat and constant elongation, often simultaneously. Selecting the construction well prevents the sagging, fading and see-through failures that generate returns.
Fibre options
- Nylon/spandex – the softest hand and best drape, excellent for fashion swim, but requires chlorine-resistant elastane for pool use.
- PBT polyester – the standard for performance and training swimwear; highly resistant to chlorine and UV, with good shape retention.
- Recycled polyester blends – now widely used in eco-positioned swim lines, with performance close to virgin PBT.
Elastane matters more than fibre
Standard elastane degrades quickly in chlorinated water. Chlorine-resistant grades, and in some cases dual-core constructions, extend garment life substantially. For frequent pool swimmers, specify chlorine-resistant elastane at 18–22% or accept a shorter replacement cycle.
Weight and structure
- Fashion bikinis: 180–200 GSM, often with a warp-knit or fine weft-knit structure.
- One-piece training suits: 200–240 GSM with higher compression.
- Board shorts: woven polyester or bonded knit, 150–200 GSM.
Higher density reduces transparency when wet, which is the most common consumer complaint about light-coloured swimwear.
UV protection
UPF ratings for swim fabric depend on fibre type, cover factor, colour and whether the fabric is wet or dry. Most PBT polyester swim knits reach UPF 50+ when dry, and drop to UPF 25–40 when wet and stretched. For childrenswear and sun-protection ranges, test in the wet and stretched state rather than the relaxed state.
Testing checklist
- Chlorine resistance after 20–40 hours of exposure.
- Colour fastness to chlorinated water, salt water and perspiration.
- Elongation and recovery, plus growth after repeated stretch cycles.
- UPF 50+ verification, wet and dry.
- Pilling and snag resistance for pool-deck abrasion.
Swim programmes reward upfront testing more than any other product category, because the failure mode is visible to the customer within weeks.
