Only the absolutely cheapest stuff is structural cardboard or particle board or MDF. One exception is probably the PAX series of wardrobe/closet system, which is relatively expensive though it's veneered particle board. The kitchen cabinets are also MDF, but relatively cheap. Definitely cheaper than most competing modular systems (that tend to also be MDF these days).
Their kitchen cabinets are definitely veneered particle board, it’s rather heavy weight and good quality particle board though, it’s comparable to quality-MDF in weight.
But a lot of their furniture is solid wood.