An important parameter to control in papermaking is the fibre mass fraction in a pulp suspension. Poor control of the mass fraction leads to an unstable process that compromises the production, quality and the energy efficiency in the pulp mill. Estimation of the mass fraction can be obtained using optical measurement techniques or ultrasound measurement techniques or a combination of both. If the fibres stems from a chemical process the fibres are beaten in a refiner. The refining influences the fibre by cutting, reshaping, removing parts of the outer fibre wall and delamination of the inner fibre wall. The motivation for this study is to examine if and how a light pulse and a sound pulse are affected by refining Two different types of chemical pulp are considered; bleached hardwood and unbleached softwood pulp. The pulp samples stems from four refining steps. At each refining step four mass fractions are mixed. The mass fraction ranges from 0.25% to 1.3%. Altogether, a set of 16 pulp samples with four refining levels and four consistency levels for each pulp type was investigated. The optical measurements were conducted using a custom designed LIDAR measurement system CMP3 from Noptel Oy, Finland. The wave length of the light was 905 nm. Both the received amplitude and time-offlight of the light pulse was recorded for each pulp sample. The ultrasonic measurements were performed in a pulse-echo setup with a pulser/receiver that excite and amplify a transducer. The transducer center frequency was 25 MHz. A freeness tester was used for measuring the influence of refining intensity on the fibres. The result shows that for unbleached softwood pulp the used measurement techniques are influenced by refining. For bleached hardwood pulp the influence of refining intensity on the tested measurement techniques was not observable or minor. The results indicate that refining can potentially influence accurate consistency estimation for unbleached softwood pulp but not for bleached hardwood pulp using the investigating measurement techniques. The result forms a base for development of a photoacoustic sensor to monitor fibre mass fraction.