Can an expert explain this? Something wrong with the chosen insulation?

I found the reverse: my insulation keeps me warm in winter and cool in summer
RT @GavinHJackson: Something I don’t quite get: if we spend a lot insulating our houses from winter do we end up sweltering in the summer and need air con? Friends in well-insulated new builds complain they were like greenhouses during the heatwave.

🐦🔗: https://nitter.eu/GreenPartyMolly/status/1565225592836034560