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Bra Cup Foam Spec for Sports and Activewear
When a bra cup has to survive a run, a spin class, or a full day of movement, the foam spec matters more than the shape. Sports and activewear cups are compressed, stretched, sweated on, and washed far harder than everyday lingerie. The three numbers that decide whether a cup holds up are foam density, ILD hardness, and ventilation, plus a fourth, yellowing resistance, for garments that get washed often. Here is how we spec PU foam cups for active programs at Senfeng, and what you should ask a supplier before ordering.
Why sports cups are a different job
Everyday cups mostly need to look smooth and feel soft. Active cups have to keep their shape after repeated high load. A cup that slowly loses rebound will gap at the seam, show press marks, and lose the support the garment promises. That is why the foam spec, not just the cup profile, is where sports programs live or die.
Density: 25 to 30 kg/m3 for stable support
We work PU foam in the 25 to 30 kg/m3 range. Below 25 the cup gets floppy and collapses under sustained compression; above 30 it turns heavy and stiff, adding weight a sports bra does not need. Within that band, a slightly higher density (closer to 28 to 30) gives the structural memory that keeps a cup from bottoming out during impact. You can review our full PU foam bra cup range to see the standard profiles we tool.
ILD: firm hold sits at 33 to 35
ILD measures the force to compress foam by 25 percent. Our practical band is 28 to 35; for sports and structured activewear we land at ILD 33 to 35. That firmer band holds the cup shape under movement and gives the locked-in feel athletes expect, without crossing into the stiff, fabric-marking territory above 35. Match ILD to the garment: 28 to 30 for light yoga and lounge-active, 33 to 35 for high-impact training. For the broader picture, see how we answer common density and ILD questions.
Vent holes: 1.5 to 2 mm, 6 to 12 per cup
Activewear lives on sweat management. Our default vent spec, 1.5 to 2 mm holes, 6 to 12 per cup, at no extra charge, does two things: it lets the foam breathe so the wearer stays cooler, and it aids clean mold release so every cup is consistent. For high-sweat programs we keep the hole pattern as part of the mold definition so it never drifts between batches.
Yellowing resistance and wash durability
Sports garments are washed often, sometimes with chlorine or strong detergent. Our cups carry 4-grade yellowing resistance so light-colored cups stay clean through storage and repeat launder cycles. It is a small spec on paper and a big one on a retail shelf.
How Senfeng supports active programs
We make PU foam molded cups by traditional thermoforming, foam placed in a heated mold at 160 to 200 degrees C, 15 to 30 tons, 8 to 15 second dwell, then trimmed and vented. With 2,000 plus existing molds, an active brand can usually match a design and get a sample in 1 to 2 days; a new mold runs 3 to 7 days, about 50 percent faster than the industry norm. MOQ is 500 pairs. Every shift logs production parameters on a batch record for full traceability, and our yield holds above 95 percent.
We hold OEKO-TEX Standard 100, GRS, and ISO 9001, and we have 8 years of export experience with zero bad debt, covered by Sinosure. That combination is what lets a buyer spec a demanding active program and trust the result at volume. Learn more about our factory and certifications.
Sports cup spec at a glance
| Spec | Senfeng standard for activewear | Why it matters in sport |
|---|---|---|
| Foam density | 25 to 30 kg/m3 | Stable support without extra weight |
| ILD hardness | 33 to 35 (high-impact) | Holds cup shape under movement |
| Vent holes | 1.5 to 2 mm, 6 to 12 per cup | Breathability and clean molding |
| Yellowing resistance | 4-grade | Stays clean through repeat washes |
| Sampling | 1 to 2 days (existing mold), 3 to 7 days (new) | Fast path from sample to production |
Frequently asked questions
What ILD is best for high-impact sports bras?
For high-impact training we recommend ILD 33 to 35. This firm band keeps the cup from losing shape under movement while staying below the 35 plus range where foam can mark delicate fabrics.
Does higher foam density mean a heavier cup?
Generally yes, which is why we keep sports cups in the 25 to 30 kg/m3 band. A slightly higher density near 28 to 30 adds structural memory without the weight penalty of going above 30.
Are vent holes necessary for sports bra cups?
Yes. The 1.5 to 2 mm, 6 to 12 per cup default improves breathability and supports clean, consistent molding, both important for garments worn during heavy activity.
Can Senfeng certify cups for export to the EU and US?
Yes. We hold OEKO-TEX Standard 100, GRS, and ISO 9001, and we have 8 years of export experience with zero bad debt, supported by Sinosure cover.
Contact us directly: WhatsApp +86 137 1289 0858 | Website: sf-bracup.com
