The pressure drop in the wick significantly affects the heat pipe heat transfer rates. This study experimentally investigated the pressure drop in wicks with spherical and irregularly shaped particles with comparisons with existing correlations to evaluate their applicability for predicting the pressure drops in wicks. Ten types of copper particles with various shapes and sizes were used to fabricate wicks using loose sintering. The particles included four spherical and six irregular particles with particle sizes from 25 ?m to 150 ?m. The results showed that the 75 ?m spherical particles had the lowest pressure drop and that the pressure drop of the irregular particle wicks decreased with increasing porosity. The Morcom correlation most accurately predicted the pressure drops in the spherical particle wicks with a mean average error (MAE) of 20.11%. For the irregular particle wicks, the Meyer and Smith correlation gave the best predictions for small particle sizes while The Morcom correlation gave the best predictions with larger particles. ? 2021 Elsevier B.V. All rights reserved. The pressure drop in the wick significantly affects the heat pipe heat transfer rates. This study experimentally investigated the pressure drop in wicks with spherical and irregularly shaped particles with comparisons with existing correlations to evaluate their applicability for predicting the pressure drops in wicks. Ten types of copper particles with various shapes and sizes were used to fabricate wicks using loose sintering. The particles included four spherical and six irregular particles with particle sizes from 25 ?m to 150 ?m. The results showed that the 75 ?m spherical particles had the lowest pressure drop and that the pressure drop of the irregular particle wicks decreased with increasing porosity. The Morcom correlation most accurately predicted the pressure drops in the spherical particle wicks with a mean average error (MAE) of 20.11%. For the irregular particle wicks, the Meyer and Smith correlation gave the best predictions for small particle sizes while The Morcom correlation gave the best predictions with larger particles.