Alpinestars Stella Plasma Chest Protector – Black

Alpinestars Stella Plasma – women's chest and back protector

The Alpinestars Stella Plasma women's chest and back protector pairs Nucleon Plasma impact padding with an anatomical sports-bra shape built for the female torso. The chest insert is certified to EN 1621-3:2018 Level 1, the back insert to EN 1621-2:2014 Level 1, and both are removable from the shell. A side zip lets you put it on with a helmet already on, and the perforated V-belt system at the waist keeps the vest in place through repeated impacts. Built for MTB enduro and downhill as well as motocross and off-road, where riders want chest and spine protection cut for a woman's body, not a resized men's fit.

Anatomical women's fit

The chest panel is shaped like a sports bra – narrower at the centre, widening out over the ribs. It solves a common problem with unisex protectors on women: a chest pad that shifts sideways or digs in on a men's cut stays put here, even when you're leaning into the bars or over a bike's tank. The stretch mesh side panels move with the torso, so the protector doesn't restrict twisting or leaning forward.

Nucleon Plasma and certification

Nucleon Plasma is a bio-based viscoelastic material (USDA-certified bio-based content) that stays soft during normal movement but stiffens within milliseconds on a fast impact, spreading the load over a larger area of the protector. Rival d3O works on the same principle – Alpinestars pairs it with its own layered structure that improves both impact performance and airflow through the material.

What do the EN 1621-2 and EN 1621-3 certifications mean?

EN 1621-2 is the European standard for back protectors – it measures how much impact force gets through to the body. Level 1 allows up to 18 kN, Level 2 up to 9 kN, so Level 2 lets less force through and is the stricter rating. EN 1621-3 is the equivalent standard for chest protectors, and the Stella Plasma meets Level 1 on both inserts. The lower the transmitted force, the lower the injury risk for the same impact.

Side zip and V-belt system

The zip runs along the side of the body, clear of the straps and out of the way in a crash, so it can't work itself open during normal movement. At the waist, the perforated V-belt system – two independently adjustable hook-and-loop straps – fits a narrower or wider waist equally well within the same size. Perforation in both the straps and the mesh panels lets air through along the whole length of the back, not just down the centre.

Removable inserts and care

Both the chest and back inserts pull all the way out of the shell, not just unclip on one side. In practice, that means you can replace a damaged insert without buying a whole new vest, and wash the textile shell on its own after a muddy or sweaty season. The Nucleon Plasma inserts themselves don't go in the washing machine – wipe them down with a damp cloth instead.

Choosing a size and layering under a jersey

Size is based on height and chest girth measured horizontally under the arms at the fullest point, not your jersey size. The S–L range together spans 169–180 cm in height and 86–98 cm in chest girth – check the size chart on the product page for the exact range per size, and size up if you're between two, so there's room for a layer underneath. The vest goes straight onto the body or over thin base layers, with a jersey on top – the mesh build and perforation are designed to be worn under outer layers, not over a jacket.

Full technical specifications are available in the Specification tab on the product page.

Frequently asked questions (FAQ)

What's the difference between Level 1 and Level 2 protection under EN 1621?

Level 1 and Level 2 describe how much impact force a protector transmits to the body. For back protectors (EN 1621-2), Level 1 allows up to 18 kN, Level 2 up to 9 kN, and chest/joint protectors follow a similar ratio. The Stella Plasma is certified to Level 1 on both zones, chest and back – enough protection for typical MTB and motocross riding, while Level 2 tends to suit dedicated downhill or racing setups.

How do I choose between size S, M and L?

Per the size chart on the product page, size is based on height and chest girth measured horizontally under the arms at the fullest point. The S–L range together covers 169–180 cm in height and 86–98 cm in chest girth. If you fall between two sizes, go with the larger one – you need room underneath for a jersey.

How does Nucleon Plasma compare to standard foam?

Standard EVA foam absorbs impact by compressing, and it stays equally soft regardless of impact speed. Nucleon Plasma is a viscoelastic material that stays flexible during slow, everyday movement but stiffens almost instantly on a fast impact, spreading the load over a larger area of the protector, then softens again once the impact has passed. The result is a protector that doesn't feel like a rigid plate during normal riding, but behaves like a hard shield in the split second it's actually needed.

Does the Stella Plasma work for MTB enduro and downhill, or only motocross?

Alpinestars lists this model under its motocross and off-road range, but the build – Nucleon Plasma inserts, CE Level 1 on chest and back, ventilated mesh vest – matches what dedicated gravity MTB protectors use as well. Enduro and downhill riders get the same certified protection level as on a motorcycle, just in a women's anatomical fit.

Do you wear it over a jersey, or underneath?

The Stella Plasma goes straight onto the body or over a thin base layer, with a regular cycling or motocross jersey on top of it. The mesh build and perforation are designed for wear under an outer layer, not over a jacket.