Can anyone help me?

Hi Sabrina

Please provide some screen shots to show what you are trying to do. Also see this video:
Search Form 2.0

Thanks Sami, I'll try to explain myself better: I have a database of products, needing to enter as many details as possible for each product, I found the Nested SubForms solution proposed by Richard very useful, so I created 4 nested subforms. Suppose I am entering the details of an athletics starting block, first I establish whether it belongs to the competition or training blocks category, then in the ProductType frm I write "Competition blocks"; then I want to define the Material Types (in this subform I indicate the types of materials whose details I will indicate, therefore: the material of the structure, the covering of the blocks); then in the frmTipoMateriale (here the name is confusing, I could have just used Material, I don't know why I didn't) I indicate the corresponding entries, so if in TipiMateriali I select "structure material" in the frmTipoMateriale I will write "aluminium", "steel", if in frmTypeMaterials I select "block covering" in frmTypeMaterial I will write "rubber", "synthetic surface", finally in the last subform, the frmProduct, after having selected the values ​​I want in the previous fields I will write the name of the product. In another form, "SubCategoriesTypeProduct", I have two cascading comboboxes that filter the query on which the subform is based and so far everything works. What I would like to do is also add the other two fields: TypeMaterials and TypeMaterial so that they filter the subform. In "Mask2" I did some tests and inserted the "TipiMateriali" and "TipoMateriale" combobox because for example I would like to see the list of competition starting blocks (TipoProdotto) whose guide material (TipiMateriali) is Aluminum (TipoMateriale), Unfortunately, however, the subform remains empty
The "Mask2" is based on the query "qryProdotti_ProdottiSottoCategorie". I attach the screenshots. I thank you in advance.

let me see if I understand you correctly.

you have a Product table let me call it ProductT.
in this product table you have the following fields:

ProductID,
ProductName,
ProductDescription etc.

ProductTypeID related to ProductTypeT (competition or training)
MaterialTypeID related to MaterialTypeT (aluminium, steel)
CoveringID related to CoveringT (rubber, synthetic surface)

Is this correct?