For a comparison, the loading of commercial CPG with 2,000 Å diameter is typically 20-30 µmol/50 mg, which is about 100 times higher than that of glass beads (Table ). The loading of the widely used peptide synthesis Wang resin is 0.3-2.5 mmol/g, which is close to 10,000 times higher. However, for long oligo synthesis, we reasoned that low loading is less of an issue. For most biological applications, as little as 1 pmol oligo is sufficient. Using glass wool, with 100 mg support, which is the quantity that can be directly used under typical small scale oligo synthesis conditions, assuming an average stepwise yield of 99.7%, which corresponds to an overall yield of 0.25% for a 2,000-mer synthesis, the quantity of full-length oligo is ~296 pmol, which is much larger than 1 pmol. However, the low percentage yield is a serious problem because there is no method to purify or concentrate the full-length oligo. For example, HPLC would not be able to resolve the full-length oligos from failure ones. Gel electrophoresis would not be able to resolve either and even if it can be engineered to resolve, the full-length oligo would be invisible on the gel due to its low percentage. Solid phase extraction methods may not be suitable for the task as well because the high entropy barrier for reactions between large molecules and solid surface would make the extraction inefficient, and it may be difficult for the large molecules to enter the pores of solid phase in the first place. However, using CBP, the low percentage problem can be overcome. With these considerations, we went ahead to synthesize long oligos on glass wool using the 800-mer GFP gene as the example.