In a time of rapid climate change, understanding what may encourage sustainable consumer behaviour is a vital but difficult challenge. Using an attitude network approach, we investigated which associations people have towards conventional and bio-based plastic in order to develop an empirically-based approach to initiate attitude- and behaviour change. With a qualitative study (N = 97), we distilled 25 evaluative reactions (i.e. beliefs, emotions, and behaviours) that encompass people’s attitudes towards using (bio-based) plastic. These reactions were used to create a new scale, which was subsequently tested among 508 online participants. The resulting data was then used to build a network displaying relationships between participants’ evaluative reactions regarding plastic use. Analyses of this network indicated that guilt was most strongly connected to people’s willingness to pay more for bio-based plastic products. Based on this, we conducted another study (N = 285) in which we experimentally manipulated guilt (general guilt, personal guilt, and control condition) to determine its effects on people’s willingness to pay for a sustainable cause. Results indicate that manipulating guilt can lead participants to donate more to a sustainable cause. This effect was fully mediated by self-reported guilt. Determining which factors influence consumers to change their buying behaviour towards sustainability is the first step in creating a demand for more sustainable products amongst the public and investors.