The fabric insulating tops prevent vapor condensation in the upper half of a flask during distillation of high-boiling materials. It also protects the flask, solutions, and laboratory from drafts, flying glass of flask implosions in high vacuum distillations, falling objects, and thermal strain between top and lower half of flask during high-temperature operations. The glass-fabric construction, laced-side opening, and elliptical hole accomodates 1-, 2-, and 3-neck flasks.