Last week, the November 2025 LEGO® Ideas set 10366 Tropical Aquarium was officially revealed. At Fan Media Days 2025 in Denmark last month, two of the creative team that brought the idea to life – the set’s designer Sven Franic (above right) and element designer Matéo Dupureur (left) – introduced the model to the assembled fan media, and stayed afterwards for some interviews where I quizzed them about the new mould developed for this set.
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10366 Tropical Aquarium
- Release date: 13 November 2025 for LEGO Insider; 16 November for all
- Pieces: 4154
Price:
- US$ 479.99 on LEGO.com US
- CA$ 599.99 on LEGO.com Canada
- GB£ 399.99 on LEGO.com UK
- AU$ 699.99 on LEGO.com Australia
- NZ$ 799.99 on LEGO.com New Zealand
- DE€ 449,99 on LEGO.com Deutschland
- NL€ 449,99 on LEGO.com Nederland
- FR€ 449,99 on LEGO.com France
- PLN 1949.99 on LEGO.com Polska
- NOK 5499,90 on LEGO.com Norge
- DKK 3499.95 on LEGO.com Danmark
“What we have is something that we've never done before,” said Sven as he revealed the product to the assembled fan media. “The way this came to be is that I was just staring at one of our colour palettes, and I thought, well... could we use all of these? Thankfully, our design process is a little bit more nuanced than that!
“Actually, one colour we didn't use for this is vibrant coral. It wasn't really intentional. It was just a colour that didn't work for us, and there’s definitely a lot more LEGO® colours that we haven't used here.”
For Sven, who previously designed some LEGO® Speed Champions sets and LEGO Icons vehicles such as 10337 Lamborghini Countach 5000 QV and 10300 Back To The Future Time Machine (see our reviews of set 10337 and set 10300 by Kev), this product presented an altogether different opportunity; one that he relished.
“It was really fun working with a lot of different colours,” Sven explained. “When you design cars, you don't often get to pick a glittery purple and stuff like that, or all these interesting elements. We really tested the shapes and colours of the LEGO® System.”
The interesting elements Sven refers to are used to create all manner of life inside the tank, but not all of them are real lifeforms. “We've taken a lot of creative liberties in creating species that are inspired more by our imagination than real fish. This is where we can really use the LEGO® medium to create something that we can't do with real life.”
To make the product even more fun and unusual, the team included some cute interactivity. “We added a few hidden functions: if you turn a rock a crab comes out, if you turn a crank, a fish wiggles around, and there’s a treasure chest that will open and close if you turn another crank. We didn't want to burden the consumer too much with technical features and gears to build a lot of LEGO® Technic stuff. We want to enjoy building nature, for the sake of it. We wanted to combine nature and put it in your living room.”
The tank has a frame and a base, but no “glass” on the sides. However, the back is solid and made entirely from azure elements, to represent water. This was the result of experimentation as to what suited this busy model the best. “When we tested what kind of environment you can place this in, it was really dependent on what was behind it,” explains Sven. “With so much colour and so much shaping going on, it really loses its silhouette once you have anything [busy] behind. So we wanted to create a background, also to give it a bit of texture and some interesting patterns of light in the water, but it has more purpose – it also serves to create stability, so I can actually pick this up, no problem.”
I was fortunate enough to be one of the fan media to speak further to Sven Franic and Matéo Dupureur, to discover more about the model’s development and its new elements.
New Elementary: Where did this concept come from, was it a brief?
Sven Franic: Yes, they wanted to do a product that was set in nature, drawing on the idea of LEGO® Botanicals, but upscaled to something really big. They had also done some consumer testing, and they really wanted a fish tank. We tried to make it as big as possible, but there's a limit when it becomes too big and starts collapsing on itself – a lot of rigidity issues and so on. So this size was kind of a ‘sweet spot’.
New E: Why are the functions so basic?
Sven: So that you don't get too immersed in building complex gearboxes and things; instead, you have time building the fun stuff. It's kind of a slow-burn experience, where you have to build a lot of base and then you get to build more and more of the fun colours and stuff.
New E: Although they’re simple, what was the biggest challenge in terms of adding the functions?
Sven: I think it's having the function set at an angle. This whole rock formation with a cave is at an angle, and so the function is also required to work at an angle. It is a little tricky to make.
New E: I’m dying to talk about the new mould. How did it come about?
Matéo Dupureur: When Sven started to build the aquarium and the fish, one of the challenges was to build the fins. They were too big, too ‘bricky’, because fins are quite supposed to be thin. We didn't have an element that worked really well, and so we saw potential in a new thin element.
New E: How did you approach the task of making a LEGO® fin piece?
Matéo: From the beginning, I saw there were different sizes of fish. So I tried to make one element that you can pattern – that was something that I wanted to achieve, that you can tessellate the elements. If you have small fish, you just use one or two. If you have bigger fish, use four of them. I tried to make an element which can be a fin, but is not too specific, so you have some potential in its versatility. I think it has good potential for creating patterns and shaping.
New E: How did the element change through the design process?
Matéo: Here's all my iterations. It started small – three modules long – and then because of the scale of the fish, we went bigger to four modules long and that was the right size, so it stayed that length. Then we turned to nailing the stacking, so it could pattern very nicely without having huge gaps, but still having a nice standalone element. It was a challenge to know the right amount of detail we should put into it. We were trying to make a body part, an organic thing, but trying to keep it looking like something that keeps some ‘LEGO® DNA’, with that flat edge.
New E: That was going to be my next question – why did you flatten this curved end? [Seen in A, B, C and F above]
Matéo:
It's because of the style of the fish, in that they are using only bricks – slopes and bows. I think that it made sense for the fin to have a flat edge. And when stacking them, it can make a more continuous line – if we had kept the rounded edge, you’d have something more divided.
New E: What about the connection point? Was there ever any exploration of clips, for example, rather than a 3.18mm bar?
Matéo: We considered that, but I think the bar gives more opportunities in the way you build.
New E: You definitely give us enough of the fins in this set to have a good play around with!
Sven: You get the fin in five colours: transparent green, transparent clear, cool yellow, aqua and reddish orange.
New E: Speaking of transparent pieces, I can’t help but notice these lovely transparent-clear brooms! Did you have to cast a new mould for this, or was it already a ‘MABS mould’? [Note: Transparent elements used to be cast in polycarbonate (PC) which required a different mould to regular ABS opaque elements. When TLG changed the transparent plastic material from PC to MABS around 2019, this meant one mould could produce both MABS and ABS elements. However, this must be planned in advance of the mould’s creation – a regular ABS mould cannot be used for MABS.]
Sven: No, that was already a MABS mould – I think no-one noticed that it is a MABS mould! Sometimes I check moulds, and I'm like, "oh, I can do that?"
New E: And this is the first opaque version of this LEGO® Super Heroes element, I think? We covered this piece a bit last year.
Sven: Yes, that was the same situation but the other way around – it had always been transparent, so we made it opaque!
Sven: And this element… I don't know what its official name is…
New E: BUSH!
Sven: …yeah, they're new in lavender. I thought that was cool, because we had this old nautical set from the 1990s [LEGO® Aquazone, 1998] that had them in red. So long ago, quite rare now, so I wanted to recolour that!
New E: A lot to enjoy here. What other elements have you worked on before this Matéo, that I might know of?
Matéo: The leaf for LEGO Botanicals; the bat cockpit for the original Batmobile; the cockpit from Ahsoka's Jedi Interceptor which is a rounded wall element used sideways; and for the Shire, I made the round window and the skirt window. There was much like discussion with the Shire window.
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| Image credits from left to right, top to bottom: Eero Okkonen, Kev Levell,©2025 The LEGO Group, remainder by Thomas Jenkins |
New E: Really? I thought that would be a quick job!
Matéo: It's funny, because the element looks super simple. It's a wall piece; you add a hole; done. But I did a lot of iteration with that element, because you want to make sure that the hole is a good size, and as well, the best position for it.
New E: How do you mean, a good size, and the best position?
Matéo: I wanted to make sure that if people want to build something that goes through the window at some point, they have the most or the best techniques. Which centre point should we use? Do you use the LEGO Technic System, do you use the LEGO System stud on the side, or do you use the top grid when using the window on its side so that it’s in the middle of four studs? There was a lot of discussion about that. There was also concern with product safety, because if there’s a hole, there is always the concern that you get a finger stuck.
New E: Well I can see we’ve definitely fallen down the rabbit hole here – we are out of time! Thanks so much for chatting to us, Matéo and Sven.
Thanks also to the adult engagement team at The LEGO Group for organising these presentations and interview sessions.
READ MORE: The Master's Return: Grantmasters' MOCs using new LEGO® elements
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