Improvements in the weight of greasy fleece (GFW) and mean fibre diameter (MED) can favour the income of alpaca producers; however, these variables are directly related, complicating the simultaneous improvement of both characteristics. Therefore, it is necessary to find new selection criteria for the simultaneous improvement of both characteristics. The purpose of the study was to characterize the fibre density (FibDen), density of hair ducts (DenDucts) and the fibre/duct ratio and No. of fibres/ducts (Fib/Duct_R) as possible selection criteria. Likewise, determine the type of relationship between them and with GFW and MFD, and construct and evaluate formal selection indices under scenarios with different available measurements, considering in all cases GFW and MFD duly weighted by their economic weights, as selection objectives. For this, fibre samples and skin images were taken, and t...