Hi Enrico10,
Most mainstream mattresses (including most innersprings) use polyfoam in the comfort layers but they are usually in softer layers and polyfoam has a very wide range of firmness/softness choices. It’s a fast response material (unlike memory foam which is a slow response material) but it’s generally not as contouring or resilient as latex which is also a fast response material.
Polyfoam mattress can have a very wide range of different “feels” and firmness or comfort levels because there are thousands of different designs and firmness levels that can be used in each layer inside each mattress but it may be worth trying some of the Ikea polyfoam mattresses if there is one near you to get a general sense of what a poly foam mattress can feel like in very general terms even though they won’t be the same as the Tuft and Needle because they use a different layering design or thickness, different types or grades of polyfoam, and different firmness levels for the polyfoam layers.
The Ikea polyfoam mattresses include …
You can also see some comments and pictures in post #3 here and post #61 here but again I would keep in mind that this would only give you a very general sense of what a polyfoam mattress can feel like but none of the Ikea mattresses have the same 3 layer design or would have the same “feel” or firmness or comfort level as the Tuft & Needle mattress.
Phoenix