A proven way is

A proven way is to cover tomatoes in the heat with grass or burlap.

Often the seedlings of tomatoes are stretched when the temperature regime is disturbed and the “tropical heat” occurs at the window. With direct sunlight, the temperature should not be higher than +25-28 ° C, and with a cloudy day it should reach a mark of less than +18-20 ° C. Otherwise, the gardener will face the “greenhouse syndrome”, in which the seedlings become pampered, sensitive to temperature changes, the stems become thinner, and the leaves become fragile.