One Piece n°1 - Black Setaria

$118.00 USD


The flagship piece of the eco-friendly collection, the one-piece with a low back.

The cup

  • Its suggestive indentation on the side does not exclude a pleasant support and provides real freedom of movement
  • The jersey is lined with our very soft material.
  • Adjustable straps that attach in 3 ways using a system of Italian knots: straight, crossed in the back or behind the neck.
  • No iron or plastic (avoid micro-waste) to adjust the straps but knots. The bows are small and comfortable to wear. On the adjustment side, the iron eyelets slide very badly on jersey materials and tend to loosen the straps too quickly; on the contrary, the knots do not loosen when you are in motion.

Size advice
To choose your one-piece size, refer to your bottom size. For example if you take 36 in panties, take S in one piece. The straps are wide adjustable and will adapt to your top.
This jersey fits normally. If you measure more than 1m70 and you hesitate between two sizes, take the size above.

In case of doubts or questions about the size, do not hesitate to write to us at

Our models
Maeva is 1m73 tall, has an A cup and wears an S (36 below).
Laetitia measures 1m76, has a B cup and wears an S (36 below).

Zita is 1m83 tall and wears a S (36 down).

Fabric & Care

Posidonia's objective is to use a fabric that contributes to cleaning the oceans and the environment, but also very elegant and comfortable to free women from any constraint of movement. An eco-responsible jersey is also a sustainable jersey, which is why I have chosen the highest range of European fabric made up of waste such as fishing nets and plastic bottles.

78% Recycled Polyamide. 22% Elastane.
Weight: 190gr.
UPF 50 (sun protection).
Bi-directional stretch (marries muscles & movements: great sensation)
Label: OEKO-TEX Standard 100.
Italian fabrics.

🌞 UV protection SPF50


The sea and the salt do not alter your swimsuits if you rinse them with fresh water after each use. Let it dry flat or laid out on its own.

Hand wash your swimsuit. You can wash it in the washing machine at the end of your vacation, on a delicate cycle (max. 30 degrees), with a non-detergent detergent, without spinning or drying cycle.

The chlorine resistance index of our materials is very good. The colors, however, are more delicate.

Customer Reviews

Based on 19 reviews
belle matière

Beau maillot, galban. Bonne qualité.
Taille petit au niveau du bas.

Cam Angot'

LE maillot noir ideal et indispensable, merci Posidonie !


C'est mon 2nd maillot 1 pièce Posidonie (le 1er acheté étant le Plongeant modèle 2021).
Comme le 1er, le Dos Plongeant a une très belle coupe ajustée qui met en valeur mes formes. En fonction de mes envies, je change la façon d'attacher les bretelles. J'adore!

Mathilde B.
Le maillot parfait

Coupe et matière au top, je suis ravie de mon achat ! Merci Posidonie 🌞

Aurelie Goumet

Simple et élégant, c'est un modèle qui me convient très bien. Livraison rapide. J'adore le cadeau utile qui est livré avec, bravo pour cette démarche écoresponsable.