For men, shirts are not allowed in temples. But for females sarees are allowed. In India, the ladies has the custom of wearing Silk saree when they go to temples during occassions. Silk clothes have the capacity to attract and store electro magnetic energy. With the friction between the body and the silk clothes, electric energy is produced, which gives rise to electro static attraction. This energy, according to shastras, would act on the mind of the devotee. It is also said that the vibrations, which are generated while worshipping, are also stored by wearing the silk clothes. The external clothing, which prevents the loss of these vibrations, would work on the mind to sustain the much needed concentration. It is also said that any worship, without concentration is useless. Hence silk clothes are preferred during Poojas. Since male doesn't wear silk, they are advised to remove shirts to observe and store the magnetic energy.